Distance determination method for use by devices in a wireless network

ABSTRACT

The performance and ease of management of wireless communications environments is improved by a mechanism that enables access points (APs) to perform automatic channel selection. A wireless network can therefore include multiple APs, each of which will automatically choose a channel such that channel usage is optimized. Furthermore, APs can perform automatic power adjustment so that multiple APs can operate on the same channel while minimizing interference with each other. Wireless stations are load balanced across APs so that user bandwidth is optimized. A movement detection scheme provides seamless roaming of stations between APs.

This application claims benefit of Ser. No. 60/449,602 Feb. 24, 2003 andclaims benefit of Ser. No. 60/466,448 Apr. 29, 2003 and claims benefitof Ser. No. 60/472,320 May 21, 2003 and claims benefit of Ser. No.60/472,239 May 21, 2003.

FIELD OF THE INVENTION

The invention relates generally to wireless networks, and moreparticularly to wireless network configuration and power leveladjustment for network performance optimization.

BACKGROUND OF THE INVENTION

The proliferation of laptop and hand-held portable computers hasproduced a concomitant need for robust, reliable, and high performancewireless networks to maximize the mobility advantages of these devicesand increase the ease of construction and management of these wirelessnetworks. Current wireless networks, such as IEEE 802.11b, 802.11a,802.11 g, (etc) networks, are subject to certain limitations that canlimit a mobile user's network performance and reliability. For instance,only a very limited number of radio channels are available. In thecurrent state of the art, wireless access points cannot effectivelyshare the same channel in the same area because of radio and controlprotocol interference. So, bandwidth over a given area is limited by thenumber of non-overlapping channels available. Also, current wirelessnetworks require manual site engineering to control the placement ofaccess points and channel distribution between access points, raisingthe cost and complexity of the wireless network installation process.Furthermore, user roaming between wireless access points isinconsistent. Once associated with an access point, a user will tend toremain associated with that access point even if another access point iscapable of providing higher performance for the user. It would bedesirable to provide wireless networking solutions which overcome theabove described inadequacies and shortcomings of current wirelessnetworks.

SUMMARY OF THE INVENTION

In accordance with the principles of the invention, various apparatus,methods, and computer program products are provided to improve theperformance and ease of management of wireless communicationsenvironments. For example, a mechanism is provided to enable accesspoints (APs) to perform automatic channel selection. A wireless networkcan therefore include multiple APs, each of which will automaticallychoose a channel such that channel usage is optimized. Furthermore, APscan perform automatic power adjustment so that multiple APs can operateon the same channel while minimizing interference with each other.Further aspects of the invention are used to cause load balancing ofstations across APs so that user bandwidth is optimized. Novel movementdetection schemes provide seamless roaming of stations between APs.These and further aspects of the invention enable the provision ofautomatically configurable, high performance wireless communicationsenvironments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communications environment in which wirelessusers interact with other networked devices via an access point (AP).

FIG. 2 shows a wireless network in which wireless user devices, orstations (STAs), access the wireless network via an access point andshare the available network bandwidth.

FIG. 3 shows a wireless network wherein the stations access the networkvia two separate access points.

FIG. 4 is a flow diagram representing how an AP builds a channel map foruse in an automatic channel selection scheme.

FIG. 5 is a flow diagram representing an automatic channel selectionmethod.

FIG. 6 is a representation of a table kept by APs for use in analternate channel selection scheme.

FIG. 7 is a flow diagram representing an alternate automatic channelselection scheme.

FIGS. 8A and 8B are flow diagrams representing a preferred embodiment ofan automatic channel selection scheme.

FIG. 9 is a representation of a Scan Table kept by APs for use in theautomatic channel selection scheme of FIG. 8.

FIG. 10 is a representation of a Channel Map kept by APs for use in theautomatic channel selection scheme of FIG. 8.

FIG. 11 is a representation of a Triplet Channel Map kept by APs for usein the automatic channel selection scheme of FIG. 8.

FIG. 12 is a representation of a Claim APs table kept by APs for use inthe automatic channel selection scheme of FIG. 8. FIG. 13 is a flowdiagram showing how an AP builds an AP KnownAPs table.

FIG. 14 is an example of an AP KnownAPs table maintained by an AP, andused for power adjustment.

FIG. 15 is a flow diagram representing the process by which an AP buildsan AP AssociatedSTA table, for use in load balancing.

FIG. 16 is an example of an AP AssociatedSTA table.

FIG. 17 is a block diagram representing a general mechanism by which anAP adjusts its transmit power backoff.

FIGS. 18A and 18B are block diagrams representing a preferred embodimentof the transmit power backoff mechanism of FIG. 13.

FIG. 19 is a table showing expected standard errors related to number ofpower level samples.

FIG. 20 is a flow diagram representing the process by which an APadjusts its transmit power backoff during STA movement.

FIG. 21 is a flow diagram representing an AP auction process, used forload balancing of STAs across APs.

FIG. 22 is a flow diagram representing the AP's handling of bids duringthe auction.

FIG. 23 is a flow diagram representing the STA initialization process.

FIG. 24 is a flow diagram representing a general mechanism by which aSTA in a wireless communications environment canvasses channels.

FIG. 25 is a flow diagram representing the preferred embodiment of FIG.20 as implemented in an 802.11 wireless networking environment.

FIG. 26 is an example of a STA Known APs table, used by STAs for poweradjustment and load balancing.

FIG. 27 is a flow diagram representing the process by which the STAKnown APs table is built by a STA.

FIG. 28 is a flow diagram representing the STA power adjustment process.

FIG. 29 is a flow diagram representing the STA Bidding process.

FIG. 30 is a flow diagram representing the process by which a STAcalculates corrected distances for use in determining whether to bid foran AP.

FIG. 31 is an example of a distance_to_rate table for use in an 802.11wireless networking environment.

FIG. 32 is an example of a rate_to_load table for use in an 802.11wireless networking environment.

FIGS. 33A and 33B are flow diagrams representing the STA bidding processin more detail.

FIG. 34 is a flow diagram representing the process by which a STAdetects its own movement.

FIG. 35 is a block diagram showing the software architectures of APs andSTAs.

FIG. 36 is a more detailed block diagram of the software architecture ofan AP implementing the invention in an 802.11 wireless networkingenvironment.

FIG. 37 is a more detailed block diagram of the software architecture ofa STA implementing the invention in an 802.11 wireless networkingenvironment.

FIG. 38 represents the encoding of a DRCP (Dynamic Radio ControlProtocol) message in an 802.11 beacon frame.

FIG. 39 represents the encoding of a DRCP message in an 802.11 dataframe.

FIG. 40 is a table summarizing the DRCP messages used in the variousaspects of the invention.

FIG. 41 is a table describing the various fields used in DRCP messages.

FIG. 42 is a diagram of the message format of a DRCP Preclaim message.

FIG. 43 is a diagram of the message format of a DRCP Claim message.

FIG. 44 is a diagram of the message format of a DRCP Announce message.

FIG. 45 is a diagram of the message format of a DRCP Bid message.

FIG. 46 is a diagram of the message format of a DRCP Accept message.

FIG. 47 is a diagram of the message format of a DRCP RegistrationRequest message.

FIG. 48 is a diagram of the message format of a DRCP RegistrationAcknowledge message.

FIG. 49 is a graph showing discrete measurements of received power overtime from the perspective of a wireless network user.

FIG. 50 is a graph showing discrete measurements of received power overtime from the perspective of a wireless network user, and showing theestimated average received power for the user within a 99% confidenceinterval.

FIG. 51 is a graph similar to FIG. 3 showing two different estimatedaverage received power measurements for small sample sizes and their 99%confidence intervals.

FIG. 52 is a graph showing two different estimated average receivedpower measurements and their 99% confidence intervals, one for a largesample size and one for a small sample size.

FIG. 53 is a graph showing a long term average measurement and a shortterm average measurement with 99% confidence interval, the comparisonshowing that it can be determined that a user has moved.

FIG. 54 is a table showing the number of samples that need to be takenin order to cause the long term average confidence interval range toconverge toward zero.

FIG. 55 is a flow diagram of the general operation of the method of theinvention.

FIG. 56 is a block diagram of an embodiment of a wireless network inwhich the invention is deployed, wherein an AP ascertains that a userhas moved.

FIG. 57 is a block diagram of an alternate embodiment of the invention,wherein a user ascertains that the user has moved.

FIG. 58 is a block diagram of one embodiment of the invention employingring buffers.

FIG. 59 is a block diagram of an alternate embodiment of the inventionemploying batched means.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In accordance with the present invention, a fully automatic controlsystem is provided for wireless communications environments. Referringto FIG. 1, a typical wireless communications environment 10 includesaccess devices 12 (one shown) that interface between a wiredcommunications medium 14 and wireless devices 16 to provide networkaccess to the wireless devices 16. Wireless devices 16 can thuscommunicate with wired devices 18 and with each other via the accessdevice 12. These access devices 12 are referred to by various namesdepending upon the wireless architecture employed, and are hereinreferred to as “access points” or “APs”. The wireless devices 16 alsohave various architecture dependent names and are herein referred to as“stations” or STAs. A wireless communications capable device may be anAP, or a STA, or both.

Various types of wireless communications environments 10 exist. Wirelesscommunications environments include for example wireless data networksand wireless I/O channels. An example of a wireless data network isdescribed in “IEEE Standard for Informationtechnology—Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements—Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)specifications—Amendment 1: High-speed Physical Layer in the 5 GHzband”, incorporated herein by reference(hereinafter “802.11”).Furthermore, various different 802.11 “modes” are defined. For example,in IEEE 802.11 compatible wireless networks, wireless devices may bearranged in an “infrastructure mode”, whereby the network is configuredsuch that STAs 16 communicate with other network devices via an AP 12,as shown in FIG. 1. 802.11 compatible devices may also be arranged in“ad-hoc” mode, whereby all the STAs 16 are within transmission range andcan communicate directly with each other. Furthermore, wireless “mesh”technologies exist, whereby each wireless device acts as both an AP anda STA. Wireless I/O channels can be used to provide I/O communications,for example, between servers and storage devices via the “Bluetooth”Standard, or between home entertainment audio and video components, orbetween wireless telephone handsets and base stations. The variousaspects of the invention apply to generally to wireless networkingarchitectures, including those used in wide area networks, metropolitanarea networks, enterprise networks, and home networks, and wireless I/Ochannel architectures, as they exist now and as they are developed.

According to aspects of the invention, an arbitrary number of wirelessaccess points (APs) can be placed in arbitrary positions, and all APsand STAs will automatically configure themselves for optimal channelusage, power levels, and STA/AP associations. So, in a wirelessnetworking environment, channel usage is optimized while interferencebetween APs is minimized. Wireless devices such as wireless enabledlaptops or hand-held computing devices or Internet protocol telephones,are transparently and seamlessly distributed between APs such thatnetwork performance is optimized from the perspective of the user of thewireless device. And, in a wireless I/O channel environment that mightbe employed for example in a home, audio, video, and other appliancesmay be moved without performance degradation, and channel usage for eachappliance may be optimized so that the appliances do not interfere witheach other.

In order to expedite the understanding of the invention, certainexamples will be described as they apply to the relatively well known802.11 wireless LAN architecture, with the understanding that theprinciples of the invention apply more generally to any wirelesscommunications environment. A preferred implementation of the inventiveprinciples will then be described as embodied in an 802.11 wirelessnetwork

The following aspects of the invention contribute to its advantages, andeach will be described in detail below.

-   -   1. AP Initialization: In many wireless communications        environments, multiple frequencies (“channels”) are available        for use by APs. For example, in accordance with 802.11b and        802.11 g, 3 non-overlapping channels are available. In        accordance with IEEE 802.11 a, 13 non-overlapping channels are        available. In an environment where multiple APs are employed, it        will be seen that it is advantageous for the APs to use        different channels to optimize performance and minimize        interference. In accordance with the invention, APs perform        automatic channel selection. Where multiple APs are distributed        in a given area, the APs execute a distributed protocol to pick        channels for each AP. APs close to each other use        non-overlapping channels.    -   1. AP Optimization:        -   a. Power Adjustment: When the number of APs in a wireless            communications environment exceeds the number of            non-overlapping channels, APs and STAs adjust their power            such that APs and STAs on the same channel can co-exist in            an area without interference. For APs using the same            channel, APs continually re-adjust their power levels based            on environmental factors such as signal strength changes due            to movement of doors, people, background noise floor, and            the like, so that the users' optimal bandwidth is maintained            without undue interference.        -   a. Auction: APs keep track of various parameters for STAs            that are associated with them, and STAs will roam between            APs for load balancing purposes, which can help to maximize            performance over a group of STAs.    -   1. STA initialization: STAs associate with an initial AP.        Invention enabled STAs turn on functions that allow them to        receive messages from invention enabled APs.    -   1. STA optimization:        -   a. Channel Canvassing: In order to further optimize            performance, STAs periodically canvass the other channels in            the band in which the STA is operating to see if a “better”            AP is present. To ascertain whether another AP is “better”,            various parameters are considered, such as signal strength            and load factors, to be further described.        -   a. Bidding: If a better AP is found, a STA enters a bidding            process to try to cause the STA to roam to the better AP.            Load balancing is thereby achieved. In addition, the bidding            process accommodates STA movement by causing the STA to            associate to a better AP after it has moved closer to the            better AP.        -   a. Power Adjustment: STAs perform power adjustment such that            they can maintain throughput to and from their currently            associated AP while minimizing the interference with nearby            wireless devices that may be using the same channel.        -   a. Movement Detection: STAs perform movement detection so            that the bidding process can be turned off while a STA is            moving, and then turned back on when the STA has stopped            moving. When turned back on, a “better” AP may turn up and            thus the STA will bid for it.    -   1. Software Architecture        -   a. The above functionality is advantageously implemented in            APs and STAs in a modular manner for ease of transfer            between platforms.        -   a. The above functionality is described in detail as it is            implemented in a preferred 802.11 network embodiment.    -   1. Movement Detection statistical analysis: A novel scheme for        highly accurate and computationally efficient detection of a        change in an attribute subject to high noise variation is        described, and applied to detection of the movement of wireless        STAs.

Since exemplary examples will refer to the 802.11 networkingenvironment, the following information provides relevant context, whileunderstandably not limiting the invention to 802.11 environments.

In an 802.11 network, APs periodically send frames called “Beacons”.STAs listen for Beacons. When an unassociated STA (i.e. a STA that isnot yet able to communicate on the wireless network) hears Beacons atwhat it deems to be a reasonable power level, it can attempt toauthenticate with the AP sending the Beacons, and then associate withthat AP. Once authenticated and associated, the STA is able to send dataframes to other STAs on the wireless network via the AP.

More particularly, APs and STAs send and respond to three differenttypes of frames, known as Class 1 Frames, Class 2 Frames, and Class 3Frames. Class 1 Frames include control frames and management frames, andcan be sent regardless of whether a STA is authenticated and associatedwith an AP. A Beacon is a type of Class 1 frame. Class 2 Frames are sentonly once a STA is authenticated, and include for example associationrequest/response messages. Class 3 Frames can be sent only ifassociated, and include data frames.

In order to maximize user bandwidth and throughput, the inventionautomatically optimizes the operation of multiple APs for a givenwireless communications environment. In accordance with the exemplaryIEEE 802.11a networking standard, 13 non-overlapping frequencies areavailable for use by the APs. Each AP is capable of transmitting andreceiving data at a maximum rate of 54 Mbps. The actual rate at whichdata is transmitted and received between an AP and a STA depends uponmany factors, including the distance between the AP and the STA, thestructures located between the AP and the STA, and the environmentalinterference occurring on the particular frequency. One skilled in theart will realize that the invention is not limited by the maximum datarates of current wireless technology, nor is it limited by currentlyunderstood radio frequency attenuation factors. The principles of theinvention will continue to be applicable as wireless technology evolves.

Consider an area such as the wireless network shown in FIG. 2, wherein 8users (shown as STAs 16), which may be mobile laptops, PDAs, and thelike, share a space including a single AP 12 operating on one of the 13available 802.11a frequencies, denoted “f1”. The 8 users 16 share thebandwidth provided by the AP 12. If all 8 users 16 are located closeenough to the AP such that the AP provides a 54 Mb bit maximum datarate, then all 8 users 16 share the AP's bandwidth such that each usermaintains 6.75 Mb throughput on average. (The invention contemplates thefact that data traffic is bursty and that a user in the present examplemay attain 54 Mb throughput for a short interval, but for purposes ofsimplicity, the average throughput over time for a given user isdiscussed.)

Now, referring to FIG. 3, a second AP 12 has been added in the area. Thesecond AP 12 operates on a different one of the 13 frequencies, denoted“f2”, such that the two APs 12 do not interfere, nor do their associatedSTAs 16. As shown, 4 of the 8 users have roamed to the second AP 12. Noweach user maintains 13.5 Mb throughput on average. Addition of furtherAPs on different frequencies further increases user average throughput.

In accordance with the invention, a Dynamic Radio Control Protocol(DRCP) provides a mechanism for an arbitrary collection of STAs and APsto automatically control the frequency and power of their radios inorder to extend the properties exemplified in FIG. 2 to maximize overallsystem performance. DRCP messages are passed between APs and APs, aswell as between APs and STAs to implement this functionality. Eighttypes of messages are used: DRCP Preclaim, DRCP Claim, DRCP Announce,DRCP Bid, DRCP Accept, DRCP Registration Request, and DRCP RegistrationAcknowledge.

DRCP Preclaim and Claim messages are exchanged between APs during APinitialization, and are used to aid automatic channel selection inaccordance with the invention. DRCP Announce messages are sent by APsand received by STAs during STA optimization. These Announce messagesinform invention-enabled STAs of available invention-enabled APs towhich they may choose to associate, and provide information about APsthat STAs can use to aid a decision as to whether to request to roam toanother AP. DRCP Bid messages are sent by STAs to APs during STAoptimization. These messages inform invention-enabled APs ofinvention-enabled STAs that are requesting association to the APs. DRCPAccept messages are sent by APs to STAs in response to DRCP Bidmessages. These messages inform a STA that it may associate with the APit is requesting to associate with. DRCP registration request andacknowledge messages are exchanged by invention-enabled APs and STAs toindicate to each that the other is DRCP capable.

The DRCP protocol employing these messages will first be described asused in a generic wireless communications environment. The detailedimplementation of each of these messages will then be further describedin terms of a preferred embodiment in an 802.11 environment.

The aspects of the invention are now described as they apply to APinitialization and optimization, and then as they apply to STAinitialization and optimization. It is noted that, though many of theinventive aspects described herein with regard to STAs and APs areadvantageous when implemented, they are not required to be implementedin a wireless communications environment. Performance advantages areachieved when only the APs, or only the STAs, or both implement one ormore of the various aspects of the invention.

-   -   1. AP Initialization

During AP initialization, APs perform automatic channel selection. Inaccordance with the channel selection aspect of the invention, APslocated in the same wireless network automatically select channels foroperation such that they do not interfere with nearby APs. The inventioncontemplates that different bands of frequencies are available, forexample based on 802.11 version and the country in which the network isdeployed. According to a preferred embodiment, APs attempt to select achannel, in each band in which the AP is equipped to operate, which isleast likely to interfere with other APs that are already deployed. APsalso quarantine channels in accordance with rules associated withregulatory domains (Europe, etc.) so they don't interfere with otherwireless applications (radar, etc.). In the event that one AP selects afree channel, and another AP selects the same free channel at the sametime (i.e. a channel selection “Collision”), the APs' media accesscontrol (MAC) addresses are used as a tie breaker. If the other AP is astandard AP that does not include the improvements associated with thecurrent invention, then the invention-enabled AP will direct its ownradio to the “next best” channel. The AP repeats the channel selectionphase for each band of frequencies.

More particularly, referring to FIG. 4, before a newly added AP 12starts to “Beacon” (i.e. broadcast management packets to other APs andSTAs), the AP 12 first examines a list of RF bands supported by the AP12, and the list of channels supported and not quarantined by the radiowhich implements the Physical Layer (PHY) for each RF band. The AP 12then selects a channel in each band according to the followingalgorithm:

For each band:

Scan Intervals occur periodically. During a Scan Interval (step 20), theAP 12 passively scans all channels which the AP supports within the band(step 22). The AP 12 gathers a list of active APs 12, the channels onwhich they are operating, and the power at which the beacons from eachAP 12 was heard. This information is used to build a table called achannel map 24 (step 26), which contains a list of all APs 12 heardfrom, the channel on which they were heard, and the signal strength atwhich they were heard. There is a separate channel map 24 for each band.The AP 12 sorts the channel map to produce a list of APs 12 in ascendingorder of power level (step 28).

Referring to FIG. 5, a channel is now selected by the AP 12 as follows.First, the AP 12 peruses the channel map (step 30), and if there is achannel on which no AP 12 is operating (i.e. signal strength=0) (step32), then the AP 12 selects that channel (step 34). Otherwise, the AP 12peruses the list for the channel transmitting the weakest signal (step36). The AP 12 now enters a time interval referred to as the “claimingperiod” (step 38).

If the AP 12 selected a channel having the weakest signal strength, theAP 12 notes the channel-ID of the channel that it has selected, thereceived power level on the channel, and the AP-ID of the AP thatgenerated that power level (step 40). It will use the power level valueas a baseline against which to detect increases in received power on itsselected channel. If the AP 12 selected an empty channel, the baselinepower level will be the AP's noise floor.

The AP 12 then advertises its intention to use the selected channel byperiodically transmitting DRCP Claim messages during the claiming period(step 42). Claim messages are transmitted at full power. During thisclaiming period, the AP 12 receives all Beacons, DRCP Claim messages,and DRCP Announce messages transmitted on the currently chosen channel(step 44) and uses the information contained therein to build an “OtherAPs” table 46 (FIG. 6, FIG. 5 step 48). For each Beacon it receives, theAP 12 notes the AP-ID and the received power level in the Other APstable 46. For each Claim or Announce message it receives, the AP 12notes the AP-ID of the AP that sent the message, the received powerlevel, and the transmit power backoff (TP backoff) in the Other APstable 46. The TP Backoff value indicates how far from maximum power thesending AP's radio has been turned down, and will be explained in moredetail in the AP Power Adjustment section. The AP 12 also marks theentry for that AP-ID as being DRCP capable. A normalized received powervalue is calculated by adding the TP Backoff value to the received powervalue. The normalized received power value equalizes the AP power levelsfor comparison purposes. When the AP 12 receives a Beacon or DRCPmessage from an AP for which it already has an entry, it updates theentry and stores the received power and TP_backoff values as a list.

If another AP 12 starts to radiate significant energy on the selectedchannel, one of two events must have occurred. The new AP 12 is eithernot running DRCP, or a conflict has occurred with another DRCP-activeAP, where a race condition has caused the other DRCP-active AP to selectthe same channel at the same time. This is called a Channel SelectionCollision (CSC).

At the end of the claim period (step 50), the AP 12 stops sending Claimmessages and evaluates the information it has collected, its CSC data,to determine if a CSC has occurred. It looks to see if the receivedpower in any entry is greater than the baseline power level it recordedfor the channel (step 52). If so, it looks to see if the received poweris exceeded in at least half of the power level values for the entry(step 54). If so, the AP 12 checks to see whether the AP in the entry isDRCP capable (step 56).

If the other AP is not DRCP active, the AP 12 defers to thenon-DRCP-active AP and starts the entire channel selection process overagain.

If the other AP is DRCP-active, then a CSC is assumed to have occurred.When a CSC has occurred, the MAC address of the other AP is compared tothe MAC Address of this AP 12. If the MAC address of this AP 12 isnumerically higher than the observed MAC address (step 58), this AP 12starts the channel selection process over again.

If at the end of the claiming period, the AP has succeeded in claimingthe selected channel, it begins running on the channel. The AP startsbeaconing, begins sending DRCP Announce messages, and prepares to enterthe Optimization stage in order to run its Auction and Power Adjustmentfunctions (step 60).

A variation on the channel selection process of FIG. 5 can be employedto improve channel selection coverage when several APs 12 are powered onall at once. Referring to FIG. 7, each AP, upon power-up, sends a claimmessage on a first channel chosen from the channel map—for purposes ofexample designated channel 1 (steps 62, 64). All APs scan all channels.All APs scanning on channel 1 will hear each other's claim messages.During the claiming period, an AP will ascertain whether channel 1 is infact available for use by it. Accordingly, the AP listens for other DRCPClaim messages on the same channel, which would indicate that anotherinvention-enabled AP is trying to use the same channel (step 66). The AP12 keeps track of the number of different APs it hears (based on AP IDsthe claim messages received) and the average signal strength of claimmessages from each AP. The AP 12 builds an adjacency vector (adjacencycount, adjacency power total) (step 68). Adjacency count represents thenumber of APs heard on the channel. Adjacency power total represents thesum of the average power levels for each AP heard. Each AP sends itsadjacency vector to all the other APs in its claim messages step 70. Ifa DRCP claim message is received (step 72), in this case on channel 1,the AP 12 first compares its adjacency count with the adjacency countreceived in the claim message (step 74). If the AP 12's adjacency countis higher than that received in the claim message, this probablyindicates that the AP 12 is closer to the center of the network. The AP12 therefore continues to claim the channel during the claim period. Ifthe AP's adjacency count is the same as the adjacency count received inthe claim message (step 76), the AP 12 then compares its own adjacencytotal power to the adjacency total power value received in the claimmessage. If the AP 12's own adjacency total power is higher than thatreceived in the claim message (step 78), this may also indicate that theAP 12 is closer to the center of the network, and therefore the AP 12continues to send claim messages on the channel. If the AP 12's ownadjacency total power is the same as that received (step 80), then theAP 12 performs the previously described MAC address test step 82). Ifthe AP 12 finds that its own adjacency count or adjacency power arelower than any received in claim messages, or that in the event of a tieon these values that its MAC address is higher, it ceases to send claimmessages on the channel and returns to peruse the channel map (step 84).Otherwise, the AP 12 continues to send claim messages including itsadjacency vector (step 70). If, at the end of the claiming period (step86), the AP 12's adjacencies are greater than other AP's adjacencies,the AP 12 has won the channel and proceeds to the AP optimization phase(step 88). According to this method, the APs closest to the center of amulti-AP network obtain the first channel assignments and subsequentchannels are assigned to the other APs.

Referring to FIGS. 8A and 8B, a preferred embodiment of the automaticchannel selection algorithm is shown. For each band:

Scan Intervals occur periodically. During a Scan Interval (step 100),the AP 12 scans all channels which the AP supports within the band,receiving Beacons and Announce messages (step 102). The informationreceived in the Beacon and Announce messages is used to build a tablecalled the “Scan table” (step 104). An example of a Scan table 106 isshown in FIG. 9. The Scan table 106 includes an entry for each AP 12from which a Beacon or Announce message has been received. For eachentry, there is stored the AP-ID and the channel on which that AP 12 washeard. Also stored is a “rxPowerRunningTotal” value that represents thesum of the signal strengths of each message received from that AP 12.Also stored is a “rxPowerSampleCount” value that represents the numberof messages received from the AP 12. A DRCP flag is set if an Announcemessage has been received from the AP 12. The entryAge entry isincremented every time the channel is scanned. The “rxPowerAvg” iscalculated during a Preclaim interval as will be further described.

As the scan progresses, the rxPowerSampleCount values in the Scan table106 are monitored, and if any one of them exceeds a threshold, hereinlabeled “threshold1” (step 108), the AP 12 proceeds to step 110 to builda channel map. In addition, if any entryAge value in the table exceeds acertain threshold “threshold2” (step 112), the AP 12 will proceed tostep 110. Also, if the number of scans completed exceeds a certainthreshold “threshold3” (step 114), the AP 12 will proceed to step 110.Otherwise the AP 12 continues scanning and updating the Scan table 106.

An example of a preferred channel map 116 is shown in FIG. 10. Thechannel map 116 contains an entry for each channel ID. To build thechannel map, the AP 12 peruses the Scan table 106 and calculates the“rxPowerAvg” value for each entry, as:RxPowerAvg[I]=Scan table[i].rxPowerRunningTotal/Scantable[i]rxPowerSamplecount;

For each channel, the AP-ID with the highest rxPowerAvg value is enteredin the channel map 116. The AP's rxPowerAvg value is entered into thechannel map 116 as the highestPwrlevel parameter.

In certain network implementations, it is undesirable to locate twooperating APs 12 within a certain distance of each other, because doingso does not increase network performance and may reduce it. So,according to a preferred option, once the channel map has beenassembled, the AP 12 checks the channel map to see if any of thehighestPwrlevel values in the map exceed a certain threshold power level(step 118). The threshold power level is chosen to indicate that the AP12 is located too close to another AP. If any highestPwrlevel exceedsthe threshold power level, the AP 12 is placed in “Standby mode” (step120). The AP 12 in Standby mode waits for a period of time hereinreferred to as “Standby Interval” before returning to start another scaninterval (step 122).

If no highestPwrlevel values are found to exceed the threshold powerlevel, the AP proceeds to assemble a triplet channel map 124 (step 126).As shown in FIG. 11, the AP 12 sorts a channel map into triplets, forexample, channels 1, 2 and 3, channels 2, 3 and 4, channels 3, 4 and 5,etc. The power heard on each channel in the triplet is averaged into atriplet average. The list of triplets is sorted in ascending order, withthe triplet with the lowest average power at the top of the list. The AP12 starts at the top of the list and looks for the first triplet inwhich the power heard on the center channel of the triplet is less thanor equal to the power heard on the two adjacent channels, and selectsthis channel (step 128). If no such triplet is available, the AP selectsthe channel with the lowest triplet average. In the example shown inFIG. 11, AP 12 chooses channel 3. This process advantageously minimizesinterference between channels by selecting channels that do not tend tohave high power adjacent channel usage.

The AP 12 then records the baseline power for the selected channel asthe highestPwrlevel value for the channel, and records the AP-ID of theAP at that power level (step 130). A Preclaim Interval is now entered(step 132). During the Preclaim interval, the AP transmits Preclaimmessages on the selected channel (step 134). The AP 12 also receivesBeacon, Announce, and Preclaim messages on the channel (step 136). TheAP 12 uses the received messages to update the Scan table (step 138).The AP 12 continues to update the Scan table until one of two Preclaimintervals expires. During the min Preclaim interval (step 140), therxPowerSampleCount value for each AP-ID on the selected channel ischecked to see if a minimum sample size threshold has been exceeded. Ifso, the Preclaiming interval ends and the AP proceeds to check to seewhether too many APs are operating on the selected channel (step 142).Otherwise, the Preclaiming period extends until the end of the maxPreclaim interval (step 144).

In some network environments, and in particular environments of limitedarea, the operation of too many APs on the same channel does notincrease network performance and may cause a performance reduction. So,according to a preferred option, the AP checks to see if there are toomany APs operating on the network (step 142). The number of differentAP-IDs present in the Preclaim APs table is used to make thisdetermination. If there are too many APs operating on the selectedchannel at a power level greater than a defined threshold, the AP 12enters Standby mode.

If there are not too many APs operating on the selected channel, the AP12 calculates an “adjacency vector sum” (step 146). The adjacency vectorsum is calculated over all APs on all channels as:Adjacency vector sum=sum(Preclaim APs[i].ReceivedPowerTotal/PreclaimAPs[i].count)The adjacency vector sum is used as a tiebreaker if necessary during theClaiming interval, to be further described.

The AP 12 now enters the Claiming interval (step 148). During theClaiming interval, the AP 12 transmits Claim messages on the selectedchannel (step 150). Claim messages include the adjacency vector sum. TheAP 12 also receives all Beacon, Announce, and Claim messages on theselected channel (step 152). The AP 12 uses the information contained inthe received messages to build a “Claim APs table” 154 (step 156). Anexample of the Claim APs table is shown in FIG. 12. The Claim APs table154 contains an entry for each AP-ID. The received power level of eachmessage received from a given AP is stored in the Claim APs table 154 asa list of values (shown as column “ReceivedPowerlevel). Furthermore, foreach Announce or Claim message received, a DRCP flag is set. The APcontinues to update the Claim APs table until the end of the Claiminginterval (step 158).

The AP 12 then evaluates the Claim APs table 154 (step 160) to ascertainwhether any other APs were heard from. If no entries exist in the ClaimAPs table 154 (step 162), the AP 12 has “won” the selected channel. TheAP 12 can then begin Beaconing and sending Announce messages on thechannel (step 164). If the Claim APs table 154 includes one or moreentries, then if the selected channel was empty at the beginning of theClaiming Interval (step 166), the AP 12 concedes the channel and returnsto re-scan (step 100). Otherwise, if the channel was not empty, then ifthe ReceivedPowerlevel values for all entries in the table are less thanthe baseline level recorded during Preclaiming plus a threshold level(e.g. 2 db) (step 168), then the AP has won the channel (step 164).However, if the AP does find a ReceivedPowerlevel value that exceeds thebaseline power level plus the threshold level, and that entry isassociated with an AP-ID that was not the one recorded on the channelduring the Preclaiming Interval, then the AP checks the entry's DRCPflag (step 170). If the DRCP flag indicates that the AP-ID associatedwith the entry is not DRCP capable, then the AP returns back to the scaninterval to re-start the channel selection process. If the DRCP flagindicates that the AP-ID associated with the entry is DRCP capable, thenthe AP compares its adjacency vector with the adjacency vector receivedin the other AP's claim messages (step 172). If the AP's adjacencyvector is less than the other AP's adjacency vector, the AP concedes thechannel and returns to re-scan. If the AP's adjacency vector is not lessthan the other AP's adjacency vector, then the AP checks to see if theadjacency vectors are equal (step 174). If they are, the MAC addressesof the two APs are compared (step 176). If the AP's MAC address isgreater than the other AP's MAC address, the AP has “won” the channel(step 164). Otherwise, the AP concedes the channel and returns tore-scan (step 100). One skilled in the art will realize that the MACaddress comparison decision is arbitrary and can be made in the oppositemanner.

-   -   1. AP Optimization

Once an AP is running on a channel, it continuously performs thefollowing functions to optimize its configuration in the wireless LAN:

-   -   Radio Power Adjustment. Each DRCP-enabled AP adjusts its power        as appropriate, to accommodate the nearest AP operating on its        channel while maintaining its connection to its farthest        associated STA. The AP conveys a TP_backoff parameter in its        Announce messages. The TP_backoff value provides an indication        of how far the sending AP has turned its transmit radio down.        This TP_backoff value is used by other APs to determine their        own TP_backoff values. A STA that is associated to the AP can        then adopt the communicated TP_backoff value to adjust its radio        power, and can track this value as it changes.    -   Auction. The AP runs the Auction process to accept new DRCP STAs        for association, as appropriate, based on received DRCP Bid        messages. These two functions are now described in terms of a        preferred embodiment.        2.a. Radio Power Adjustment        2.a.1 AP Maintained Tables

In order to perform Radio Power Adjustment, the AP 12 maintains a numberof tables. The tables include information received from other APs andSTAs operating on the selected channel. This information is used toascertain such things as power levels of other devices on the channel,and distances between devices on the channel, in order to control theAP's power level.

2.a.1.1 AP KnownAPs Table

Each AP 12 maintains a number of tables that it consults to performpower adjustment. One such table is the AP KnownAPs Table 200. As shownin FIG. 13, once initialized on a channel, an AP 12 receives Beacons andDRCP Announce messages from all other APs 12 operating within the rangeof its radio, on its channel (steps 202, 204, 206). The AP 12 uses thesereceived messages to build the AP KnownAPs table 200. For each messageit receives, the AP 12 checks to see if it has an entry in the APknownAPs table for the AP-ID in the message (step 208). If found, the AP12 updates the entry (step 210), otherwise it creates a new one (step212), up to a maximum of Max_APs entries (step 214). The value of Max_APis design dependent.

Referring to FIG. 14, the AP 12 stores the following fields in thecorresponding AP knownAPs table 200 entries:

-   -   AP-ID    -   TP Backoff    -   Max Power    -   DRCP capable    -   Age    -   Normalized power    -   Sample size    -   Corrected power

The AP-ID, TP Backoff, and Max Power fields are extracted from each DRCPAnnounce and Hello message received. The TP Backoff value is stored as alist of values for each message received from each AP-ID. The samplesize is the number of TP Backoff values received for each AP-ID.

Since Announce messages are only sent by DRCP-enabled APs, the AP 12also marks the entry as DRCP-active. APs sending Beacons which containno DRCP fields are not marked DRCP-active. For each message received,the AP adds the TP Backoff value to the received power level todetermine a normalized received power level, as follows:normalized_power=avg(received_power+tp_backoff);

Accounting for the TP backoff in the normalized power level provides avalue that is consistent and can be used for comparison with power levelmeasurements from other APs.

Received beacons do not explicitly carry a TP backoff value, however,since beacons are always transmitted at full power they effectivelycarry a TP backoff value of zero. Thus, the AP 12 can update the APKnownAPs table 200 based on a received Beacon. In this case the AP 12stores the TP backoff value as zero, and sets the normalized power andthe Max Power to the received power level value.

Additionally, the AP 12 keeps an Age for each entry. The Age is reset tozero, “0”, each time a Beacon or DRCP Announce is received from the APcorresponding to the entry. Entries are aged as part of the AP PowerAdjustment process.

2.a.1.2 AP AssociatedSTAs Table

APs 12 also continuously maintain a table of the STAs 16 that areassociated with it—the AP AssociatedSTA table. Referring to FIG. 15, forevery associated STA 16, the AP 12 monitors and collects signal strengthinformation for data packets received (step 220). If an entry for theSTA already exists in the AP AssociatedSTAs table (step 222), that entryis updated (step 224). Otherwise a new entry is created for the STA(step 226). The collected data is periodically analyzed by the AP for APpower adjustment purposes. In addition, whenever a DRCP-active STA 16becomes associated with an AP 12, it sends a Registration Requestmessage to the AP 12. Registration Request messages are sent by the STA16 to the AP 12 periodically until a Registration Acknowledge message isreceived by the STA 16. Upon receipt of a Registration Request from anSTA 16 (step 228), the AP 12 updates the entry in the AssociatedSTATable and marks it as a DRCP-active STA (step 230) and sends aRegistration Acknowledge message to the STA 16 (step 232).

As shown in FIG. 16, the AP 12's AP AssociatedSTA Table 240 maintainsthe following information about each STA:

-   -   STA-ID—MAC Address of the Station    -   Quiet-time—A value representative of the amount of time since        data was last received from this STA    -   DRCP-Active—defaults to false, set to true upon receipt of a        Registration Request    -   Distance—Distance (in Banzais, to be further described) to this        STA, calculated based on signal strength information and TP        Backoff    -   Max Power—list of power values    -   Power samples—number of power samples received    -   Normalized_power    -   Corrected_power    -   sta_load_factor—The load of this STA on this AP, see section        4.c.        2.a.1.3 AP Power Adjustment

During the channel selection process, the AP 12 transmits at maximumpower, that is, it uses a TP backoff value of zero. Once the AP 12 hassuccessfully claimed a channel, it calculates a TP Backoff value andadjust its transmit power for data transmissions down, in accordancewith this value to minimize same channel interference and maximizechannel/bandwidth re-use. The calculation of the TP Backoff value is nowfurther described.

Generally, with reference to FIG. 17, AP power adjustment isaccomplished as follows: The AP 12 peruses its AP KnownAPs table (step260). The AP 12 finds the AP in the table with the highest TP Backoffvalue. The AP 12 then sets its own Max TP backoff value to the highestTP Backoff value (step 262). This Max TP Backoff value, if used as theAP 12's TP Backoff value, would reduce the AP 12's transmit power to alevel just below the range of the nearest AP operating on the samechannel.

Once the Max TP backoff is calculated, the AP then scans theAssociatedSTA table to ascertain the distance to the farthest associatedSTA 16 (step 264). The distance to the farthest associated STA 16 iscompared to the distance to the closest AP 12 operating on the samechannel (step 266). If the distance to the farthest associated STA 16 isless than the distance to the closest AP 12, the AP's TP Backoff valueis left at Max TP Backoff (step 268). If the distance to the farthestassociated STA is greater than the distance to the closest AP operatingon the same channel (step 266), then the Max TP backoff value isadjusted back down to accommodate this STA (step 270), and the AP's TPbackoff is set to this adjusted value (step 272). This power adjustmentis periodically repeated to account for changes in the AP KnownAPs tableand the AP AssociatedSTAs tables change (step 274). Power adjustment maybe repeated every second, for example, in an 802.11 environment.

In accordance with the preferred embodiment for use in a wireless datanetworking environment, as shown in FIGS. 18A and 18B, APs perform theabove described power adjustment as follows. First, AP 12 checks to seeif its Avoid Other WLANs flag is set (step 280). The Avoid Other WLANsflag is a configuration parameter which can affect Power Adjustment. Inmany wireless networking architectures, it is possible for several APsto occupy the same channel while serving different physical networks.For example, in the 802.11 architecture, several APs can serve differentESSs. The Avoid Other WLANs flag is false by default. When set to false,the AP 12 will ignore any other APs on the same channel who's physicalnetwork is different from this AP 12's physical network (e.g., ESS ID).This option is useful for cases when there are multiple APs inrelatively close proximity that are on different networks. In this case,the operator may prefer to run his AP at the maximum power level toprovide the best possible signal for all stations on his network.

If the Avoid Other WLANs flag is not set, the AP 12 sets its TP Backoffto 0 (step 282). The AP 12 will therefore transmit at full power as longas the Avoid Other WLANs flag is not set. If the Avoid Other WLANs flagis set, the AP proceeds with the power adjustment process and will notinterfere with other APs even if they are operating on a differentnetwork.

The AP 12 processes the information in the AP KnownAPs table every HelloInterval (step 284), to perform power adjustment. The Hello Interval isarchitecturally and design dependent. In an 802.11 environment, theHello Interval may be for example the 100 ms beacon interval. TheknownAPs table entries are first aged before other processing isperformed. The age of each entry is incremented (step 286), and anyentries whose age exceeds Max AP Entry Age are deleted (steps 288, 290).Thus, if an AP hasn't been heard from in a while, it is aged out of thetable to prevent it from affecting this AP 12's power adjustmentcalculations.

As previously described, the normalized power field of an entry, “n”, ofthe AP KnownAPs table is determined by averaging over several receivedpower measurement samples. The greater the number of samples used toderive the value, the more accurate the measurement. The AP accounts forthe inaccuracy in this value by subtracting a standard error, based onthe sample size, from the normalized power level, as shown in thefollowing formula. Note, in an 802.11 environment, the normalized powerlevel is expected be a negative number, ranging in value from −25 to −90dBm.AP knownAPs[n].corrected_power=APknownAPs[n].normalized_power—getStandardError(sample_size);

In this formula, the function “getStandardError” would return thestandard error for the sample size of “sample_size” in each entry “n”.For example, table I in FIG. 19 shows the standard error values for anumber of sample sizes for RF signal measurements. This formula isapplied to each entry “n” in the AP KnownAPs table to calculate thecorrected_power values for each entry (step 292).

The AP KnownAPs table is then scanned for the entry corresponding to theAP which was heard at the highest corrected_power level. Thiscorrected_power level is compared to the AP 12's noise floor (step 294).(The AP's noise floor is a measure of background power on the channel.)If the AP 12 finds that the highest corrected_power level is less thanthe AP 12's noise floor, then the AP 12 may transmit at maximum powerwithout interfering with the other APs on the channel. It thereforeleaves its Max TP Backoff value at 0 (step 296). If the AP 12, however,finds that the highest corrected_power level is higher than the AP 12'snoise floor, it needs to set a TP Backoff to avoid interfering with thatAP. In this case the AP 12 calculates Max TP Backoff by subtracting itsnoise floor from the corrected_power associated with that AP (step 298).

Once it has calculated Max TP Backoff, the AP 12 must then determine ifthere are any associated STAs 16 that are farther away (ie who's signalstrength is weaker than) the highest_power_AP. The AP 12'sAssociatedSTAs table is analyzed to find the STA 16 that is the greatestdistance from the AP (step 300). The normalized_power and sample sizevalues for this STA are used to calculate a corrected_power value forthis STA as previously described. The lowest power STA's corrected_powerlevel is compared to the AP 12's noise floor (step 302). If thecorrected_power level is less than the noise floor, then the AP 12 needsto run at full power to cover the STA, so the AP TP Backoff value is setto 0 (step 304). If the corrected_power level is greater than the AP12's noise floor, then the STA TP Backoff value is set to thecorrected_power level minus the noise floor (step 306).

Next, Max TP Backoff is compared to STA TP Backoff (step 308). The AP'sTP Backoff (“my TP Backoff”) is set to the lower of the two backoffvalues to avoid interference with the closest AP while ensuring coveragefor the farthest STA. So, If STA TP Backoff is less than Max TP Backoff,then my TP Backoff is set to the Max TP Backoff value (step 310). If STATP Backoff is greater than Max TP Backoff, then the my TP Backoff valueis set to the STA TP Backoff value plus some minimum signal-to-noiseratio (step 312).

The AP 12 then adjusts its transmit power by the value of my TP Backoff(step 314), and uses my TP Backoff as the value of TP Backoff in itsAnnounce messages. According to the preferred embodiment, the AP willtransmit data at a power level adjusted by TP Backoff, but will transmitDRCP management messages (e.g. Claim, Announce, Accept) at fall power.So, APs can always hear management messages passed between each other.

Furthermore, various different wireless networking architectures mayprovide a mechanism for clearing the wireless channel, furtherincreasing the probability that the management messages will bereceived. For example, in the 802.11 architecture, the AP issues a Clearto Send (CTS) message to clear the channel (step 316), and then sends aDRCP Announce message at maximum power (step 318). After sending theAnnounce message at maximum power level, the AP resumes use of itscalculated TP backoff value for data packets to minimize same-channelinterference, as described above.

2.a.1.3.i AP Power Adjustment During Station Movement

When a STA 16 is associated with an AP 12, the AP 12 keeps track of thedistance between the STA 16 and the AP 12. If the AP 12 is using anon-zero TP Backoff value, and the AP 12 ascertains that the STA 16 ismoving out of range of the AP 12 at backed off power, then the AP 12 canadjust its TP Backoff value to accommodate the STA 16's movement.

The distance between an AP 12 and an associated STA 16 is calculated andstored in the AssociatedSTAs table in units of “Banzais”. The Banzai isa unit of distance derived from a measurement of received signalstrength from an AP 12 operating with a known transmit power backoff. Inan 802.11 environment, for example, a received signal strengthmeasurement is generally expected to range in value from −25 dBm to −90dBm, but depending upon possible antenna gain at the high end orsensitivity at the low end, may range from 0 dBm down to −100 dBm. Atransmit power backoff is generally expected to range in value from 0 dBto 65 dB. Given a received signal strength measurement of“received_power” and transmit power backoff of “TP Backoff” from an AP,the distance to that AP in Banzais is calculated as follows:distance_in_banzais=ABS[MIN[0, (received_power+tpbackoff)]]

Algorithms for movement detection are described in more detail later.For purposes of AP power adjustment, as previously described, the AP 12collects multiple samples of received_power and TP Backoff values foreach STA 16 over time, and the distance between the AP and the STA iscalculated over all these samples. The AP 12 detects movement bycontinuously checking to see if the difference between the distance toeach station, derived from a set of long term samples, is sufficientlysmaller that the current distance measurement based on the most recentlycollected samples, to indicate that the STA 16 is moving away from itsAP 12.

If the AP 12 detects that the STA 16 is moving away and the STA 16 iswithin a given Short Term Standard Error Banzais of the current edge ofthe transmit signal (based on the current TP Backoff), then the AP 12switches to a TP Backoff of 0 until it no longer has any moving STAsassociated with it.

More particularly, referring to FIG. 20, to detect STA movement, the AP12 collects a long term samples of distance values for a STA 16 (step320), and then continuously collects short term sample size distancevalues for the STA 16 (step 322). The difference between the long termdistance and short term distance values is compared to a MovingThreshold value plus the standard error in the two distance measurementsin order to eliminate false movement detection. (See section 6 for moreinformation.) A station is considered to be moving when the short termdistance exceeds the long term distance by more than the MovingThreshold plus the sum of the errors in the two measurements. Thefollowing pseudo code describes this comparison.

IF ((AssociatedSTAs[n].short_term_distance −AssociatedSTAs[n].distance) >   (movingThreshold + longTermStdError +shortTermStdError))   (step 324) THEN   moving = TRUE (step 326) ELSEmoving = FALSE; (step 328) If the AP 12 detects that the STA 16 ismoving, the AP 12 sets its TP Backoff to 0so that it transmits data at maximum power (step 328). The AP 12 remainsat maximum power until it detects that the STA 16 is no longer moving,or quiet. If the AP 12 determines that it is no longer moving before theSTA 16 loses the association to its AP, the AP 12 resumes normalprocessing of received signal strength to determine a new appropriate TPBackoff value as previously described (step 334).

Once the AP 12 detects that the STA 16 is moving, it begins usinganother test to detect when the STA 16 has stopped moving. To detectthat the STA 16 has stopped moving, the AP 12 compares the distance tothe STA 16, derived using the Long Term Sample Size, to the distancederived from the most recent Short Term Sample Size samples. The AP 12looks to see when this difference is less than just the standard errorin the two measurements to determine that the STA 16 has stopped moving.This test is performed as follows (step 330):

IF ((AssociatedSTAs[n].short_term_distance −AssociatedSTAs[myAP].distance) < (longTermStdError + shortTermStdError))THEN   moving = FALSE; (step 332)2.b AP Auction

The purpose of the Auction is to accomplish the distribution of STAs 16across APs 12 in a manner that optimizes wireless communicationsperformance. The goal is to have STAs 16 associate to their nearest AP12 while taking loading (the sum of the individual loads of the STAs 16already associated to the AP 12) into account. This allows the RFfootprints of the APs 12 and STAs 16 to be minimized, while ensuringthat no AP 12 is overloaded.

STAs 16 learn of available APs 12 through the Announce messagestransmitted by the APs 12. As will be further described with regard toSTA optimization, a STA 16 calculates a “biased distance” to each AP 12it hears from, including its own AP, using the received power andloading information from the Announce messages. A STA 16 will send a Bidmessage to an AP that is “better” than the STA's current AP, wherebetter means that the AP has a lower biased distance. The Bid messagecontains the value of the difference between the biased distance fromthe STA 16 to the destination AP 12 and the biased distance to the STA16's current AP. This value is called the biased distance delta.

In particular, referring to FIG. 21, the AP 12 collects any receivedBids over a period of Auction Interval (steps 340,342). If a Bid isreceived from a STA 16 from which a Bid has already been received (step344), the new bid information replaces the previous bid information(step 346). Otherwise a new entry is created for the STA 16 (step 348).In either case the bid entry's age is reset (step 350).

At the end of Auction Interval (step 352), the AP 12 processes thereceived bid information. (The Auction Interval in an exemplary 802.11environment may be on the order of, for example, 7.5 seconds.) The ageof all bid entries is incremented by one (step 354) and then any bidentry whose age is greater than Max Bid Age is deleted (step 356). Thelist is then sorted by biased_distance_delta value (step 358).

The AP 12 selects the bid entries with the highest biased distance deltavalues, up to acceptsPerAuction entries, and sends a DRCP Accept messageto each of the STAs 16 corresponding to those entries (step 360). TheIDs of each STA 16 being sent an Accept is put in a list of outstandingaccepts (step 362), and a count of accepted STAs who have not yetassociated and registered is noted as numAcceptsOut (step 364). At thispoint the next auction period begins.

In addition to receiving DRCP Bids, the AP 12 also receives anindication any time a STA 16 associates to the AP 12. Referring to FIG.22, on receipt of the indication (step 366), the AP checks to see if ithas bid information from the newly associated STA 16 (step 368). Any bidinformation found for the newly associated STA 16 is deleted (step 370).The AP 12 also checks to see if the STA 16 is in the list of outstandingaccepts (step 372), and if the STA 16 is in the accepts outstanding listthat entry is deleted (step 374) and the numAcceptsOut count isdecremented (step 376). At the end of the Auction Interval, anyoutstanding accepts from the previous auction cycle are considered tohave timed out, hence the list of outstanding accepts is emptied andnumAcceptsOut is reset. These processes continue as long as the AP 12 isactive on a given channel.

3. STA Initialization:

The purpose of the STA initialization phase is to find and associate toa suitable AP 12 to provide the STA 16 with access to the wireless LAN,and to prepare for the operation of the DRCP protocol and algorithms.

Referring to FIG. 23, when started, the STA 16 produces a list ofchannels supported by the STA 16 (step 380). In multi-PHY-variant STAs(e.g., STAs supporting multiple bands such as 802.11a/b/g), the channellist will include all of the channels that are supported across thevarious supported bands.

First, the STA 16 scans for beacons on all channels across all supportedbands (e.g., STAs supporting multiple bands such as 802.11a/b/g willscan all channels in each of the a, b, and g bands.) (step 382) The AP12 that is received at the greatest signal strength is selected (step384).

Preferably, where multiple bands are supported, the selection of an AP12 also takes into account a preference for the higher bandwidth bandsso that, for example as implemented in an 802.11 environment, an AP 12on an 802.11a or 802.11 g channel is given some preference to oneoperating on an 802.11b channel.

Once an AP 12 is chosen, the STA 16 authenticates and associates to thatAP (step 386). Any security policies that control association areexecuted at this point.

During initialization, the STA 16 also enables the DRCP protocol so thatthe STA 16 will receive DRCP Announce messages (step 388). The STA 16then proceeds to the STA optimization phase (step 390).

4. STA Optimization

Once it has made its initial association and has access to the wirelessLAN, the STA continuously performs the following functions to optimizeits configuration:

-   -   Canvassing. The STA periodically tunes its radio to listen on        other channels, while retaining its association to its AP on its        operating channel. This canvassing of other channels is done to        allow the STA to receive DRCP Announce messages from APs        operating on other channels.    -   Bidding. The STA receives and processes DRCP Announcements from        all APs that are operating within its range on any of its        supported channels. It evaluates the received power and loading        information from the Announce messages and if it finds an AP to        which it would be more optimally associated than its current AP,        the STA makes a bid to move to that AP.    -   Radio Power Adjustment. The STA adopts the TP Backoff value        communicated in Announce messages from its AP, tracking this        value as it changes.    -   Movement Detection. The STA continuously checks to see if it is        moving away from the AP to which it is currently associated. If        it detects that it is moving, it stops participating in the DRCP        bidding process and adopts a process of next AP selection that        is invoked when the association to its AP degrades.

These functions are described more particularly as follows:

4. a STA Canvassing

The process by which the STA 16 canvasses the other channels todetermine whether to send a DRCP Bid message is now described in furtherdetail. In order to monitor DRCP Announce messages, a STA 16periodically tunes its radio to the channels other than the one to whichit is currently associated. However, the STA 16 must remain associatedto its current AP 12 so that it does not lose data packets. So, packetsmust be buffered during the time that the STA 16 is canvassing. Variouswireless communications architectures may provide different means forpacket buffering.

Generally, referring to FIG. 24, during a periodic scan interval (step400), the STA 16 causes the AP 12 to which it is currently associated totemporarily buffer the packets destined for the STA 16 (step 402).Packet buffering can be initiated in a variety of ways. For example, theSTA 16 may send a DRCP message to the AP 12 to cause the buffering, orthe AP 12 may periodically turn on buffering and notify the STA 16 thatit has done so. While the STA 16's packets are being buffered, the STA16 tunes its radio to another channel and listens for Beacons and DRCPAnnounce messages on that channel (step 404). This information is usedby the AP 12 to determine whether to bid for another AP. When the scaninterval is complete, packet buffering is turned off and the STA 16receives its buffered packets from the AP 12 (step 406).

FIG. 25 sets forth a STA canvassing mechanism for use in an 802.11wireless networking environment. The 802.11 architecture convenientlyprovides a power save mode that, in accordance with the principles ofthe invention, can be used for this purpose.

The 802.11 power save mode is intended for use by STAs 16 so that theycan turn off their radios for periods of time in order to save power.STAs 16 can indicate to APs 12 that they are entering this power savemode. In response, APs 12 buffer the STAs' packets while the STAs 16 are“sleeping”. APs 12 periodically send special Beacon messages to the STAs16. STAs 16 wake up in response to these special Beacon messages. TheseBeacon messages include information as to whether any data is bufferedfor the STA 16. The STA 16 “wakes up” if data is buffered for it.

STAs 16 operating in an 802.11 environment in accordance with thepreferred embodiment of the invention use the 802.11 power save mode togo off-channel and canvass other channels for DRCP Announce messages.After the channel canvass is complete, the STA 16 reverts to normalpower save mode. Stations that have not been set to Power Save Mode bymanagement are caused by the STA 16 to act as if they've been set to thePower Save Mode. STAs 16 that have already been set to Power Save Modeby management will have even more time to canvass.

In particular, referring to FIG. 25, at the start of a scan interval(step 410), the STA 16 inquires about the current state of its powersave mode. The power save mode that was set by management (active, powersave) is remembered (step 412). The power save mode is set to powersave, and the listen time (time the STA 16 stays asleep), if any, isincreased by a period of time herein referred to as scan time (step414). At the beginning of the power save cycle, the STA 16 actuallystays awake temporarily, instead of dozing as it told the AP it wasgoing to do. It is during this time that other channels are canvassedfor beacons and DRCP Announce messages (step 416). After the canvass isdone the STA 16 resumes its power save cycle (step 418). This processrepeats every scan interval. Whenever the STA 16 is not canvassing, itrestores the remembered management set power save mode. The scaninterval may be for example twice per Beacon interval.

Stations that have not been set to Power Save Mode by management arecaused by the STA 16 to act as if they've been set to Power Save Mode,with listen interval set to the minimum value (i.e., every Beacon). STAs16 that have already been set to Power Save Mode by management will havethe most amount of time to canvass.

During the canvass time the STA 16 tunes its radio to a differentchannel in order to passively listen for beacons and DRCP Announcemessages. The STA 16 keeps track of which channels have been canvassed,stepping through all of the channels until all supported channels havebeen canvassed. The STA 16 keeps track of all DRCP Announce messages,and the power level at which they were received.

4.a.1 STA KnownAPs Table

The STA 16 receives beacons and DRCP Announce messages from all APs 12within the range of its radio. These are processed to build a table ofall known APs 12, the “STA knownAPs” table 430, as shown in FIG. 26. TheSTA knownAPs table includes the following parameters for each entry:

-   -   AP-ID    -   age    -   Channel ID    -   Load factor    -   TP Backoff    -   Max Power    -   Distance_samples    -   Distance    -   My_load_factor    -   Biased_distance

The STA Known APs table 430 is built as shown in FIG. 27. For eachBeacon or Announce message received (steps 432, 434), the STA 16 checksto see if it has an entry in the STA KnownAPs table 430 for the AP-ID inthe message (step 436). If found, the STA updates the entry (step 438),otherwise it creates a new one (step 340), up to a previously setmaximum herein referred to as Max APs entries (step 442).

The STA 16 stores the following fields from received beacons in the STAknownAPs table entries:

-   -   AP-ID    -   Channel ID    -   Max Power

The STA 16 stores the following fields from received Announce messagesin the corresponding STA knownAPs table entry:

-   -   AP-ID    -   Channel ID    -   Received Power    -   Load Factor    -   TP Backoff

The STA 16 also notes the received power level that accompanied thebeacons and Announce messages and uses these values along with the TPbackoff values to calculate the distance to the APs in Banzais, aspreviously described. (Again, since non-DRCP APs will always sendbeacons at full-power, the TP Backoff value for these is set to 0.).

The Received Power and TP Backoff entries are lists, where each entry ineach list corresponds to a Beacon or Announce message received for thecorresponding AP-ID. The received power level value and correspondingly,the distance in Banzais, are subject to variability in the RF channel.The STA 16 saves a number of these distance measurements for each entryin the knownAPs table, so that it can use averaging to compensate forthis variance, to be further described. For its own AP (i.e. the AP towhich the STA is currently associated), the STA 16 averages over arelatively large number of distance values, herein referred to as “LongTerm Sample Size” distance values. For all other entries, the STA usesfewer, “Bid Sample Size”, distance values.

Additionally, the STA keeps an Age for each entry. The Age is reset tozero, “0”, each time an Announce message is received from the APcorresponding to the entry. Entries are aged as part of the STA Biddingprocess, described below.

4.b STA Power Adjustment

Referring to FIG. 28, an associated and registered STA 16 receives allAnnounce messages from the AP 12 to which it is associated. Upon receiptof an Announce message (step 556), the STA notes the TP Backoff value inthe Announce message and adopts that value as the STA's own TP Backoff(step 558).

4.c STA Bidding

Each time the STA Canvassing function completes a canvass of allchannels, the STA 16 analyzes the information in the STA knownAPs tableto see if there is a potential “better” AP 12 with which to associate.The notion of what constitutes a better AP takes into account thedistance to the AP in Banzais, the available data rate, and the loading(number of associated STAs) on the AP, if known.

Referring to FIG. 29, the STA Bidding process operates generally asfollows. When the canvass is complete and a sufficient number of sampleshave been collected on each channel (step 450), the STA knownAPs table330 entries are aged before other processing is performed (step 452).The age of each entry is incremented, and any entries whose age exceedsMax AP Entry Age are deleted (step 454). Since the age field is clearedeach time an Announce message or Beacon is received, this aging processwill eliminate APs from whom nothing has been heard for “Max AP EntryAge” bidding cycles.

As mentioned, the STA 16 uses averaging to compensate for variance inits distance measurements. It requires Long Term Sample Size distancevalues for the STA knownAPs entry corresponding to its AP, before itperforms further processing of the table (step 456). Once the STA 16 hasLong Term Sample Size distance values for its own AP, it then waitsuntil it has Bid Sample Size distance values for all entries in theknownAPs list at that time before it begins looking for a better AP(step 458). This is to avoid making a decision to move to a new APbefore it has sufficient information about the other APs in the network.However, to avoid the potential for waiting indefinitely, it will notdelay processing the knownAPs list for any new APs that were added afterit has Long Term Sample Size distance values for its own AP.

Working with the entries for which there are sufficient distancemeasurement samples, the STA 16 looks for a potential better AP. Insummary, a biased distance is calculated for each entry, which takesinto account the available data rate as well as the loads on the APs(step 460). The data rate is deduced based on the received signalstrength and the technology being used (i.e., in an 802.11 environment,the 802.11 mode of operation (a,b,g)). After calculating the biaseddistances for all of the entries in the STA knownAP table, the AP withthe lowest biased distance is considered to be the best candidate and,if it appears better than its current AP (step 462), a Bid is sent (step464).

More particularly, referring to FIG. 30, for each entry “n” in the STAknownAPs table (denoted KnownAPs[n]), the following processing isperformed on entry knownAPs[n]. An index of “myAP” corresponds to theentry for the AP to which the STA is currently associated, i.e.,knownAPs[myAP] is the entry for the STA 16's current AP.

As previously described, the distance field in the STA knownAPs table430, knownAPs[n].distance per entry, is the distance in Banzais, to thecorresponding AP, averaged over a number, Bid Sample Size, ofmeasurement samples. As previously noted, this value is subject tovariance in the RF channel. The bid selection process should preferablyyield the choice of a “better” AP only when the new AP actually wouldprovide better performance for the STA, and not when the new AP simplyappears to be better due to this variance. The variance in the new AP'sdistance measurement is represented by a “Bid Sample Std Error” valuerelated to the bid sample size, and the variance in the current AP'sdistance measurement is represented by a “Long Term Std Error” valuerelated to the long term distance sample size. It is advantageous tominimize the error in the distance measurement for a given entry n, incomparison to the STA's current AP. This is done by using a correcteddistance that is set to the distance to the STA's current AP, if theentry falls within the sum of the standard errors on the two distancemeasurements. The corrected distance, “corrected_distance”, isdetermined as follows:

IF ( ABS [knownAPs[n].distance − knownAPs[myAP].distance] ≦   (BidSample Std Error + Long Term Std Error) ) (step 470) THEN  corrected_distance = knownAPs[myAP].distance (step 472) ELSEcorrected_distance = knownAPs[n].distance; (step 474)4.c.1 Distance to Load Factor Conversion

The corrected distance to each AP 12 is recorded in the STA knownAPslist. This distance is then used in conjunction with data related to theparticular wireless environment in which the AP 12 is operating toderive an estimate on the expected load factor for the STA. For example,in an 802.11 environment, the distance and 802.11 mode (a,b,g) are usedto retrieve the expected data rate for the STA 16 from thedistance_to_rate table:

knownAPs[n].data_rate = distance_to_rate [knownAPs[n].mode ]           [knownAPs[n].corrected_distance ] ;         (step 376)An example of distance to rate calculations for 802.11 modes is shown inTable II in FIG. 31.

Then, the expected load for this datarate is retrieved from therate_to_load table:knownAPs[n].my_load_factor=rate_to_load[knownAPs[n].data_rate ]; (step478).

An example of a rate_to_load table for 802.11 networks is shown in TableIII in FIG. 32. One skilled in the art will realize how to implementdistance-to-rate and rate-to-load tables from specifications for otherwireless environments. The corrected_distance and my_load_factorparameters are determined in this manner for each entry n in the STAKnown APs table 430.

Any entries in the knownAPs list that represent non-DRCP APs need to begiven default values for their load_factors so that they can beconsidered by the Stations for associations as well. These defaultload_factors are derived from a default number of STAs per AP value thatshould be consistent across the network and a default “average datarate” per technology. That is:

if (knownAPs[n].DRCP_Enabled == FALSE) then   knownAPs[n].load_factor =STAs_per_AP *   rate_to_load [ default_rate [ knownAPs[n].mode ] ];

When determining the load of the STA 16's current AP (myAP), when myAPis a non-DRCP AP, then its default load_factor value is preferablyincremented by the STA's load on that AP. This helps to support aconsistent view of the load of that AP both before and after a STAassociates with it—that is, since the STA adds its own load to thedefault load of its prospective (non-DRCP) AP before it makes a decisionto associate with it, it must also add its load to the default load forthis AP after it has associated with it.

4.c.2 Biased Distance Calculation

Using the my_load_factor to the AP 12, the load_factor currently on theAP 12 (received from Announce messages) and the corrected distance tothe AP 12, the STA 16 calculates a biased_distance value to account forthe loading on the prospective AP 12 in comparison to the loading on theSTA 16's current AP, as shown in FIG. 29. The biased distance iscalculated as described by the following formula:

knownAPs[n].biased_distance =   knownAPs[n].corrected_distance *  (knownAPs[n].load_factor+knownAPs[n].my_load_factor)/    knownAPs[myAP].load_factor)   (step 490)

Next, a biased distance to the STA 16's current AP 12 is calculated toaccount for the loading on the current AP 12 relative to the loading onthe prospective AP. This calculation is made as follows:

knownAPs[n].my_ap_rel_biased_distance =   knownAPs[myAP].distance *  knownAPs[myAP].load_factor/  (knownAPs[n].load_factor+knownAPs[n].my_load_factor)   (step 492)Finally, the difference between the biased distance to the prospectiveAP and the relative, biased distance to the STA 16's current AP isdetermined, as follows:

  knownAPs[n].biased_distance_delta =    knownAPs[n].my_ap_rel_biased_distance −    knownAPs[n].biased_distance (step 494)After calculating the biased_distances and biased_distance_deltas forall of the APs in the knownAPs list, the STA 16 checks to see if any ofthe biased_distance_delta values are positive (step 496). If not, thenthe STA 16's current AP is still the best AP, so the STA 16 remainsassociated with its current AP (step 498). Of any positivebiased_distance_delta values, the best AP is the one with the highestpositive biased_distance_delta value (step 500). If the best AP is notDRCP enabled (step 502), then the STA 16 associates with that AP (step504). If the best AP is a DRCP AP (step 502), then a Bid is sent (step506) and the STA 16 resumes normal operation until it either receives aDRCP Accept or it completes another Canvass Sample Number passes of allchannels. If there is more than one AP with the same highestbiased_distance_delta values (step 508), the STA 16 checks to see if anyof them is the last AP to which it Bid (step 510) and if so, it selectsthat one again (step 512).

If a DRCP Accept is received with the AP-ID matching the selected APsAP-ID (step 514), the STA sets its TP backoff value to zero (step 516)and associates with the AP from which the Accept was received (step518). The STA 16 now sends a DRCP Registration Request to the AP (step520) and starts a timer (step 522) to go off every Registration TimeoutInterval. When the timer expires (step 524), the STA 16 sends outanother DRCP Registration Request and resets the timer. Upon receipt ofa DRCP Registration Acknowledge (step 526), the timer is disabled (step528).

If no DRCP Accept is received (step 414) in response to the STA's Bidmessage after a certain period of time (step 530), the STA remainsassociated with its current AP.

After the STA 16 has associated with a new AP, the STA 16 waits until ithas collected a large number, Long Term Sample Size, of distancemeasurements to its new AP before it resumes this process of evaluatingthe knownAPs table for bidding.

4.d STA Movement Detection

When a STA 16 is associated with an AP 12, the STA 16 receives DRCPAnnounce messages from all APs 12 within the range of its radio.Referring to FIG. 34, once the STA 16 has collected Long Term SampleSize of distance measurements from Announce messages received from itsAP 12 (step 540), it can begin the movement detection process.

The STA 16 continuously collects Short Term Sample Size distance valuesto the current AP (step 542). To detect movement, the STA 16 comparesthe distance to its AP 12, derived from averaging over the long termusing Long Term Sample Size, to the short term distance, derived fromaveraging the most recent Short Term Sample Size samples. Thisdifference is compared to a Moving Threshold value plus the standarderror in these two measurements in order to eliminate false movementdetection. A station is considered to be moving when the short termdistance exceeds the long term distance by more than the MovingThreshold plus the sum of the errors in the two measurements. Thefollowing pseudo code describes this comparison.

IF ((knownAPs[myAP].short_term_distance − knownAPs[myAP].distance) >  (movingThreshold + longTermStdError + shortTermStdError)) (step 544)THEN   moving = TRUE (step 546) ELSE moving = FALSE; (step 547)

Once the STA 16 detects that it is moving (step 446), and as long as theSTA 16 does not detect that it has stopped moving, the STA 16 refrainsfrom participating in the bidding process (step 548), seeking a new APonly if warranted by the deterioration of its current association. Ifthe STA 16 determines that it is no longer moving before the STA 16loses the association to its AP, the STA 16 resumes normal operationincluding participation in the bidding process.

As in movement detection, to detect that the STA 16 has stopped moving,the STA 16 compares the distance to its AP 12, derived using the LongTerm Sample Size, to the distance derived from the most recent ShortTerm Sample Size samples. The STA 16 looks to see when this differenceis less than just the standard error in the two measurements todetermine that the STA 16 has stopped moving. The following pseudo codedescribes this test.

IF ((knownAPs[myAP].short_term_distance − knownAPs[myAP].distance) <  (longTermStdError + shortTermStdError)) (step 550) THEN   moving =FALSE (step 552)If the STA 16 determines that it has stopped moving, the bidding processis restarted (step 554).5. Software Architecture

In accordance with the preferred embodiment, the previously describedfunctionality is implemented in software in APs 12 and STAs 16respectively. Referring to FIG. 35, the software is implemented inaccordance with a layered architecture, such that it contains a platformdependent module that interacts with a platform independent module. Thisarchitecture is advantageous for porting the inventive functionalitybetween different wireless architecture platforms. As shown each AP 12includes a platform independent module 560 that interacts via an AP API562 with an AP platform dependent module 564. Likewise, each STA 16 (oneshown) includes a STA platform independent module 566 that interacts viaa STA API 568 with a STA platform dependent module 570. In environmentswhere the APs 12 are connected to each other via a wired network 14,DRCP messages may be passed directly between the APs 12 via the wirednetwork 14. In environments where the APs are interconnected via onlythe wireless network 15, APs 12 interact with each other and with STAs16 by passing DRCP messages to the respective platform dependent layer,which causes wireless platform specific protocol messages to be passedbetween the APs 12 and STAs 16 to implement the DRCP protocol.

Referring to FIG. 36, there is shown a representation of the AParchitecture of FIG. 35 as it applies to in an 802.11 networkingenvironment. The AP Radio Management Agent (ARMA) 580 is the platformindependent layer of the software. The AP Radio Manager (ARM) 582 is theplatform dependent layer of the software. The ARM software is actuallyimplemented within several different 802.11 platform specific elementsof the AP. More information on these elements can be found in theincorporated 802.11 specification.

Referring to FIG. 37, the Station Radio Manager (SRM) 584 is theplatform dependent portion of the STA software. As shown, the SRMcommunicates with various 802.11 platform specific elements. The StationRadio Management Agent (SRMA) 586 is the platform independent portion ofthe STA software. Likewise, the AP radio manager is the platformdependent portion of the AP software, communicating with 802.11 platformspecific elements. SRMAs communicate with ARMAs through the use of DRCPmessages as previously described.

These DRCP messages are now described in further detail. Generally, DRCPmessages could be encoded as standard LLC data frames, and the inventiondoes not preclude such an implementation. But, according to thepreferred embodiment as implemented in an 802.11 networking environment,DRCP management messages are encoded as new types in existing Class 1Frames. DRCP messages are addressed either to a Group MAC Address, or toan individual MAC address, and are distinguished by the presence of theDRCP Protocol Identifier in the Protocol Identification Field of a SNAPPDU.

The DRCP messages are now described in detail as they operate on an IPWLAN. Some DRCP messages are transmitted as IEEE 802.11 MAC managementframes of subtype Beacon on the wireless LAN only, while others aretransmitted as data frames encoded as LLC 1 Unnumbered SNAP PDUs on thewireless LAN or the wired/wireless network between APs.

FIG. 38 shows the encoding of a DRCP message in an IEEE 802.11 Beaconframe. The DA field is set to a specific DRCP group MAC address asappropriate to the message type, and the BSS ID is a DRCP specificBSS-ID. The fixed portion of the Beacon frame is as defined in the802.11 standard, and the variable portion of the frame is replaced bythe information element created to carry a DRCP protocol message. Inaccordance with a preferred embodiment, it is desirable for DRCP enabledAPs to perform automatic channel selection and load balancing byexchanging DRCP Claim, Preclaim, and Announce messages in managementframes of subtype Beacon, while preventing STAs from attempting toassociate with an AP in response to receipt of one of these messages.Several steps are therefore taken in addition to the DRCP protocolspecific address fields already mentioned. First of all, the “ElementID” field includes an OUI specific to the DRCP protocol, which alertsDRCP enabled APs and STAs that the frame holds a DRCP message.Furthermore, standard (non-DRCP) 802.11 Beacons include in the body ofthe frame field certain fields such as “Supported Rates”, “FH ParameterSet”, “DS Parameter Set”, “CF Parameter Set”, etc. (Refer to theincorporated 802.11 standard document for more information.) Managementframes of type Beacon encoding 802.11 Claim, Preclaim, and Announcemessages either do not include these fields, or set them to a nullvalue. Non-DRCP STAs that might otherwise attempt to use the DRCP Beacontype frames for association cannot do so due to the lack of thisinformation.

FIG. 39 shows the encoding of a DRCP message within an 802.11 MAC Dataframe, of subtype Data. DRCP messages are addressed either to anindividual MAC address or to one of the DRCP Group MAC addresses, andare distinguished by the presence of the DRCP Protocol Identifier in theProtocol Identification Field of a SNAP PDU. DRCP messages that aretransmitted over the DS may be formatted as shown, or may be similarlyencoded in another MAC data frame depending upon the DS media.

In accordance with the preferred embodiment, the SRMAs and ARMAsinteract with the SRMs and ARMs to generate and/or collect informationneeded to produce or interpret DRCP protocol messages. It is noted thatthe DRCP protocol could be implemented over non-802-11 primitiveswithout departing from the principles of the invention. The followingdescribes the primitives used in an 802.11 environment.

5.a Enhancements to Standard 802.11 MAC Service Interface

The ARMAs and SRMAs transmit and receive DRCP messages over a standard802 MAC Service Interface, with some enhancement. The receive interfaceis enhanced in both the STA and the AP to allow the SRM and the ARM toindicate to the SRMA and ARMA respectively, the power at which DRCPmessages are received. In particular, the semantics of the 802.11MA-UNITDATA.indication service primitive are modified as shown by theunderlined text, to add a received power parameter as follows:

MA-UNITDATA.indication ( source address, destination address, routinginformation, data, reception status, priority, service class, receivedpower )

The received power parameter specifies the signal strength, expressed indBm, at which the MSDU was received. The received power value indicatesthe current level at which the sending device is heard, but does notprovide an indication of whether or not the sending device istransmitting at full power. The potential power level at which a devicemight be heard can be determined when the transmit power backoff (i.e.,the amount, in dB, by which the radio is turned down) in use by thedevice is also known.

5.b Enhancements to the Standard 802.11 Management Interface

BSS Description

The BSSDescription Parameter contains a list of elements that describethe BSS. An additional element is added to this list:

Name Type Valid Range Description Received Power Integer −1 to −99Indicates the power (in dBm) at which the Beacon from this BSS wasreceived.Send DRCP

This mechanism is provided to allow the ARMA to send DRCP Messagesencoded in 802.11 Management frames of type Beacon.

MLME-SENDDRCP.request

This primitive is used by the ARMA to request that the ARM send a DRCPMessage over the wireless media, encoded in an 802.11 Management frameof type Beacon. As shown in FIG. 34, this is a special type of Beaconframe wherein the fixed portion of the Beacon frame is as defined as inthe 802.11 standard, and the variable portion of the frame is replacedby a single information element that carries the DRCP message.

The primitive parameters are as follows:

MLME-SENDDRCP.request   ( Destination Address Message Length DRCPMessage Quiet Channel CTS Duration ) Name Type Valid Range DescriptionDestination MAC Address N/A A specific DRCP group MAC Address address asappropriate to the message type. Message Length Unsigned 0 . . . 2312Indicates the number of octets Integer in the DRCP Message field. DRCPMessage DRCP N/A DRCP Message Message Quiet Channel Boolean FALSE (0),Indicates whether the STAs TRUE (1) associated to the AP should bequieted for the Beacon transfer by the transmission of a Clear To Send(CTS) frame immediately prior to the Beacon transfer. CTS Durationunsigned 16 . . . 255 _sec Indicates the value to be integer placed inthe duration field of the CTS frame. The value represents the time, inmicroseconds, required to transmit the pending Beacon frame, plus oneshort interframe space (SIFS) interval. This parameter is only used whenthe quiet channel parameter is true.

This primitive is generated by an ARMA to request that a DRCP Message besent on the wireless media encoded in an 802.11 Management frame of typeBeacon. DRCP Claim and Hello messages are sent in this manner. Aspreviously described, the ARMA may optionally quiet the channel beforesending a DRCP Hello message by first by sending a CTS frame. Inparticular, if the Quiet Channel parameter is TRUE, the ARM transmits aClear To Send (CTS) frame immediately prior to the Beacon transfer. TheDRCP Hello CTS Destination MAC Address is placed in the Receiver Address(RA) of the CTS frame. The duration field of the CTS is set to the valueof the CTS Duration parameter.

The fixed portion of the Beacon frame is as defined in the 802.11standard. The DA is set to the Destination Address parameter value, theSA is the AP's MAC address, and the BSS ID is the DRCP Default BSS-ID.The variable portion of the frame is replaced by a single informationelement with an Element ID of DRCP Protocol, with a Length field valueof the Message Length parameter and the Information field containing theDRCP Message.MLME-SENDDRCP.confirm

This primitive confirms the transmission of a DRCP message to the ARMA.The primitive parameters are as follows:

MLME-SENDDRCP.confirm   ( ResultCode ) Name Type Valid Range DescriptionResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME-SENDDRCP.request NOT_SUPPORTED

This primitive is generated by the MLME as a result of anMLME-SENDDRCP.request to send a DRCP message encoded in an 802.11Management frame of type Beacon. The ARMA is thus notified of the resultof the Send DRCP request.

Power Management Fib

As previously described, one way that a STA can support periodiccanvassing is to indicate to the AP that it is in power save mode,thereby causing the AP to buffer the STAs packets while the STA iscanvassing. This mechanism supports a STA's ability to indicate to theAP that it is in power save mode, without actually going into power savemode.

MLME-POWERMGTFIB.request

This primitive requests the SME to use the power save mode interactionwith the AP to allow time to canvass other channels. The primitiveparameters are as follows:

MLME-POWERMGTFIB.request ( ) Name Type Valid Range Description Null N/AN/A No parameters

This primitive is generated by an SRMA to cause the MLME to borrow partof the doze time (if the STA is in power save mode) or all of the dozetime (if the STA is in active mode) in order to canvass other channels.

This request causes the SRM to:

-   -   1. save the current power management mode settings    -   2. set:        -   a. power management=Power_Save        -   b. WakeUp=FALSE        -   c. ReceiveDTIMs=FALSE    -   3. signal the AP that it is using power management mode.

This request prepares the SRM to:

-   -   1. at the start of the power save cycle, signal the SRMA by        sending an MLME-PSSTART.indication while actually keeping the        power on.    -   2. catch any user or net manager power mode management        operations and cause them to use the saved settings, not the        active settings.        MLME-POWERMGTFIB.confirm

This primitive confirms the change in power management mode to the SRMA.The primitive parameters are as follows:

MLME-POWERMGTFIB.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME-POWERMGMTFIB.request NOT_SUPPORTED

This primitive is generated by the MLME as a result of anMLME-POWERMGTFIB.request to mimic power save mode. The SRMA is thusnotified of the change of power mode indicated.

Power Save Start

This mechanism notifies the SRMA that it can begin to canvass.

MLME-PSSTART.indication

This primitive indicates to the SRMA the start of the power save cycle.The STA does not actually power off its radio and enter the sleep stateat this point, but preferably, it should not transmit outgoing framesafter sending this indication until it receives anMLME-PWRMGMTFIBCONTINUE.request. The primitive parameters are asfollows:

MLME-PSSTART.indication ( ) Name Type Valid Range Description Null N/AN/A No parameters

This primitive is generated by an SME to indicate the start of powersave cycle. The SRMA is thereby notified of the start of the power savecycle.

Power Management Restore

This mechanism further supports a STA's ability to indicate to the APthat it is in power save mode, without actually going into power savemode.

MLME-P WRMGMTRESTORE.request

This primitive tells the MLME that it should restore the user-configuredpower save mode. This primitive allows the SRMA to tell the MLME that itno longer needs to lie to the AP about power save (that control overpower save is passed back to the MLME). The primitive parameters are asfollows:

MLME-PWRMGMTRESTORE.request ( ) Name Type Valid Range Description NullN/A N/A No parameters

This primitive is generated when the canvass mechanism is taken out ofservice. The receipt of this primitive causes the SRM to restore thesaved power management mode settings and:

-   -   1. if saved power mode was ACTIVE, immediately force the awake        state;    -   2. if saved power mode was POWER_SAVE, continue normal power        save mode operation.        MLME-P WRMGMTRESTORE.confirm

This primitive confirms the change in power management mode to the SRMA.The primitive parameters are as follows:

MLME-PWRMGMTRESTORE.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME.PWRMGMTRESTORE.request NOT_SUPPORTED

This primitive is generated by the MLME to confirm that the SME hasexecuted an MLME-PWRMGMTRESTORE.request. It is not generated until thechange has been indicated. Upon receipt of this primitive, the SRMA isnotified of the change of power mode indicated.

Power Management Fib Continue

Once canvassing is complete, this mechanism informs the SRMA that it“has control” of the radio and communicates power save state (awake ordoze).

MLME-PWRMGMTFIBCONTINUE.request

This primitive tells the MLME that it's safe to enter the awake stateand transmit frames if desired. The primitive parameters are as follows:

MLME-PWRMGMTFIBCONTINUE.request   ( ) Name Type Valid Range DescriptionNull N/A N/A No parameters

This primitive is generated when the SRMA is has completed canvassing.Upon receipt, the MLME enables transmission of user data frames, ifnecessary.

MLME-PWRMGMTFIBCONTINUE.confirm

This primitive confirms the change in allowed power management state.The primitive parameters are as follows:

MLME-PWRMGMTFIBCONTINUE.confirm   ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME.PWRMGMTFIBCONTINUE.request NOT_SUPPORTED

This primitive is generated by the MLME to confirm that the SME hasexecuted an MLME-PWRMGMTFIBCONTINUE.request. It is not generated untilthe change has been indicated. Receipt by the SRMA serves asnotification of the change of the allowed power save mode.

Channel Out

This mechanism supports the ability to indicate to an ARMA that achannel has gone out of service.

MLME-CHANNELOUT.indication

This primitive reports to the ARMA that a channel that was previouslyavailable has become unavailable. The primitive parameters are asfollows:

MLME-CHANNELOUT.indication ( Channel ) Name Type Valid Range DescriptionChannel Integer 0-255 Channel identifier

This primitive is generated by the MLME when a channel becomesunavailable. Receipt of this primitive causes the ARMA to remove thechannel from its channel map.

Channel In

This mechanism provides the ability to indicate to an ARMA that achannel has gone into service.

MLME-CHANNELIN.indication

This primitive reports to the ARMA that a channel that was previouslyunavailable has become available. The primitive parameters are asfollows:

MLME-CHANNELIN.indication ( Channel ) Name Type Valid Range DescriptionChannel Integer 0-255 Channel identifierThis primitive is generated by the MLME when a channel becomesavailable. Receipt of this primitive causes the ARMA to add the channelto its channel map.Beacon Notify

This mechanism supports the ability to detect any other APs using thesame channel.

MLME-BEA CONNOTIFY.request

This primitive requests the MLME to notify the ARMA whenever a beacon isreceived. There is one indication for each Beacon received. Anindication is generated any time a Beacon is received on the currentchannel. The primitive parameters are as follows:

MLME-BEACONNOTIFY.request ( Notify Enable ) Name Type Valid RangeDescription Notify Enable Boolean True or False When True, indicatesthat the PIOTE is to be notified of any Beacons received. When False,this mechanism is to be disabled.

This primitive is generated by an ARMA when it wants to be notified ofany beacons received on its own channel. Receipt of this primitive by anMLME causes the MLME to enable a mode whereby the ARMA will be notifiedif any Beacon is received.

MLME-BEACONNOTIFY.confirm

This primitive confirms the change in the beacon notification mechanism.The primitive parameters are as follows:

MLME-BEACONNOTIFY.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME-BEACONNOTIFY.request NOT_SUPPORTED

This primitive is generated by the MLME as a result of anMLME-BEACONNOTIFY.request. Reciept of this primitive by the ARMA servesas notification of the change of Beacon Notify as indicated.

MLME-BEA CONNOTIFY.indication

This primitive reports to the ARMA that a Beacon was received on thedata channel. The primitive parameters are as follows:

MLME-BEACONNOTIFY.indication ( BSSDescription ) Valid Name Type RangeDescription BSSDescription BSSDescription N/A The BSS Description(including any additional Description Elements defined in 0) pertainingto an individual Beacon that was received.

This primitive is generated by the MLME if a beacon is received on thedata channel. Note that a separate MLME-BEACONNOTIFY.indication isgenerated for each beacon received, so the primitive parameter will onlyever contain a single BSSDescription. Upon receipt of this primitive,The ARMA is notified of the Beacon and the signal strength at which itwas received.

5.c DRCP Messages Preferred Implementation

The following describes the manner in which the above describedprimitives are used to implement DRCP messages in an 802.11 environment.FIG. 40 shows a summary of the DRCP messages that are used to implementthe previously described functionality. FIG. 41 shows field definitionsused in DRCP messages, as follows:

DRCP Preclaim

FIG. 42 shows the format of the DRCP Preclaim message. A DRCP Preclaimmessage is encoded in an 802.11 Management frame of type Beacon. TheARMA sends a DRCP Preclaim message using the MLME-SENDDRCP.requestmanagement primitive with the following parameters:

-   -   Destination Address—DRCP All ARMAs Group MAC Address        -   Message Length—12            -   DRCP Message—Preclaim Message                -   Quiet Channel—FALSE (0)                -   CTS Duration—0                    DRCP Claim

FIG. 43 shows the format of the DRCP Claim message. A DRCP Claim messageis encoded in an 802.11 Management frame of type Beacon. The ARMA sendsa DRCP Claim message using the MLME-SENDDRCP.request managementprimitive with the following parameters:

-   -   Destination Address—DRCP All ARMAs Group MAC Address        -   Message Length—16            -   DRCP Message—Claim Message                -   Quiet Channel—FALSE (0)                -   CTS Duration—0                    DRCP Announce

FIG. 44 shows the format of the DRCP Announce message. A DRCP Announcemessage is encoded in an 802.11 Management frame of type Beacon. TheARMA sends a DRCP Announce message using the MLME-SENDDRCP.requestmanagement primitive with the following parameters:

-   -   Destination Address—DRCP All Agents Group MAC Address        -   Message Length—16            -   DRCP Message—Announce Message                -   Quiet Channel—FALSE (0)                -   CTS Duration—0                    DRCP Bid

FIG. 45 shows the format of the DRCP Bid message. A DRCP Bid message isencoded as an LLC 1 Unnumbered SNAP PDU in a data frame. The message isaddressed to the Individual MAC Address of the AP in which the targetARMA is instantiated. The SRMA sends a DRCP Bid message over thestandard MAC Service Interface.

DRCP Accept

FIG. 46 shows the format of the DRCP Accept message. A DRCP Acceptmessage is encoded as an LLC 1 Unnumbered SNAP PDU in a data frame. Themessage is addressed to the Individual MAC Address of the STA in whichthe target SRMA is instantiated. The ARMA sends a DRCP Accept messageover the standard MAC Service Interface for relay to the DS.

DRCP Registration Request

FIG. 47 shows the format of the DRCP Registration Request message. ADRCP Registration Request message is encoded as an LLC 1 Unnumbered SNAPPDU in a data frame. The message is addressed to the Individual MACAddress of the AP in which the target ARMA is instantiated. The SRMAsends a DRCP Registration Request message over the standard MAC ServiceInterface for relay to the DS.

DRCP Registration Acknowledge

FIG. 48 shows the format of the DRCP Registration Acknowledge message. ADRCP Registration Acknowledge message is encoded as an LLC 1 UnnumberedSNAP PDU in a data frame. The message is addressed to the Individual MACAddress of the AP in which the target SRMA is instantiated. The ARMAsends a DRCP Registration Request message over the standard MAC ServiceInterface for relay to the DS.

6. Movement Detection

As previously described, APs and STAs ascertain movement based uponevaluation of short and long term averages of parameters, along withexpected error measurements. In accordance with an aspect of theinvention, movement detection is achieved through application of abroader inventive concept that provides a way to ascertain the dynamicattributes of a system based upon short and long term averages ofdiscrete data measurements. The principles of this invention apply toany system in which a discretely measured variable may change widely.For purposes of clarity, however, the invention is now described interms of its particular application to wireless networks.

In a wireless network such as the one shown in FIG. 1, a wirelessnetworking user (heretofore also referred to as “STA”) is associatedwith an access point (AP). The AP provides associated users with networkconnectivity via radio frequency (RF) signals. Various APs are used toprovide seamless RF coverage, so that when the user moves away from oneAP toward another AP, the user will associate with the closer AP (or theAP that is more lightly loaded) and seamless network functionality isthereby maintained. It is therefore important to be able to ascertainthe location of a user relative to an AP so that a determination can bemade as to whether the user is currently moving. This allows the systemto assure that the user rapidly becomes associated with the closest APso the overall system performance is maximized. As a user moves towardor away from an AP, the received power level (i.e. the power of the RFsignal received by the user from the AP) goes up or down respectively.Thus, one way to ascertain user movement is by monitoring received powerlevels.

However, received power levels can appear to vary greatly even when auser is not moving. For example, the opening or closing of a doorway cancause either a gain or attenuation in the user's received power level. Aperson waving their hand near the user's antenna can even cause a gainor attenuation in received power level. Environmental interference canalso cause changes in received power levels. These various changes inpower level can cause a user to appear to be moving when in fact he orshe is not. This can cause the user to roam needlessly between APs,particularly in environments where APs are close together and theirtransmit power levels are lower than maximum power. Alternatively,variations in signal power due to these effects can mask the fact thatthe user is indeed moving. In this case, the system could fail to detectthe motion and fail to associate the user with the appropriate AP. FIG.49 shows an example graph of discrete measurements of received power vs.time for a user who is not moving. As can be seen, the inaccuracies indata sampling prevent any assumption of movement in one direction or theother.

As a more particular example, consider an 802.11a wireless network. APsin such a network provide a maximum bandwidth of 54 Mbps. Bandwidthdrops with distance from the AP. Assume that adjacent APs have theirtransmit power adjusted so that each provides a 54 Mbps cell on theorder of about 10 feet in diameter. A walking user might be able totransition through such a cell in 2 seconds. On the other hand, a usersitting at his desk (near the center of the cell, right next to the AP)who gets up and leaves travels only 5 ft, not 10 ft to the edge of thecell—so, it may take the user only just over a second to be in the aisleand out of the cell. These examples provide a motivation for why rapidpower estimates based on discrete measurements must be made. Increasingsampling rates increases accuracy, but this also causes more overhead interms of wireless channel bandwidth, interrupt activity and processingoverhead on the user device. Some user devices could be simpleappliances such as phones, digital assistants, etc. and have verylimited processing power. So a trade-off must be made between samplerate and overhead.

According to one possible implementation, power levels are measured atintervals over a window of time and a roaming decision is made. In an802.11a network, when a user is about 1 ft from an AP whose power is setso that it has a 54 Mbps cell which is about 10 ft in diameter, theuser's true mean power level should be about −38 dbm. Assume a 99%confidence interval around the true mean (i.e. the power level to beestimated) is desired. Yet, there is a variability to the measurementsbecause of environmental effects (hand waving, etc.) as well as inherentinaccuracy in the implementation measurement itself. Assume theseinaccuracies and statistical variability in the data result indistribution of the data with a standard deviation, σ=15 dbm. Referringto FIG. 50, if only 8 samples are taken in such a statisticaldistribution, then the 99% confidence interval around this (true) meanis −23.4 dbm to −52.6 dbm.

The 99% confidence interval has a range of |52.6−23.4|=29.2 dbm, orabout 30 dbm. This is about ±15 dbm. So, because of the variability inthe signal, if only 8 samples are taken, all that can be known is thatthe “true power” lies somewhere between −23.4 dbm and −52.6 dbm and thatsuch conclusion can be drawn with 99% assurance.

If less accuracy can be tolerated, for example 95% or even 90%confidence, the resultant range would be narrower. But, lower confidenceintervals increase the likelihood of “false positives”. A false positiveoccurs when a user is ascertained to be moving when in fact he or she isnot, causing the user to needlessly roam to another AP. It is desirableto minimize such false positives as they needlessly consume valuablebandwidth.

When a user doubles his or her distance from an AP, the user's receivedpower decreases by 6 db. So, when a user moves from 1 foot away to 2feet to 4 feet away from the AP (almost to the edge of the cell), the(true) average received power has decreased from −38 dbm to −44 dbm to−50 dbm respectively. But, as seen in FIG. 51, when trying to estimatethe average received power from eight samples taken during this motionwith a 99% confidence interval in the data, it cannot be ascertainedthat the user has moved. This is because the true mean is reallyunknown. All that is known is that it lies somewhere between −23.4 dbmand −52.6 dbm. So, when only these few samples are taken, it cannot beascertained whether the user is moving away from the AP, getting closerto the AP, or not moving at all.

Of course increasing the number of samples taken decreases the range oferror. If 20 power samples are taken, then the 99% confidence intervalis −29.1 dbm to −46.9 dbm. But, taking lots and lots of samples willtake too long unless channel overhead is increased.

Now consider taking n samples to produce an estimate, and then taking nmore to produce a second estimate. The two estimates are then comparedto see if a conclusion can be drawn as to whether the user is moving. Ifthe confidence intervals around each estimator are large, e.g. 99%, thenthere exists a spectrum of outcomes and again it cannot be ascertainedas to whether the user is moving toward or away from the AP, or notmoving at all. In FIG. 51, to tell that the user is moving away from theAP with 99% assurance, the upper edge of the right confidence intervalmust be positioned below the lower edge of the left confidence interval.

Consider two basic scenarios regarding motion in wireless networks:

-   (1) The user stays in one place for a reasonable time and then moves    to a new place. The user requires communication while moving, but,    the user tends to move and then stop and stay somewhere for a while.    Or similarly, the user may move very slowly within one confined    area, and then move more rapidly to another area.-   (2) The user is constantly in motion.

In the instance of scenario #1, which describes the very large majorityof user activity in wireless networks, the accuracy of the powerestimate can be greatly improved. In accordance with the principles ofthe invention, two averages of the received signal strength aremaintained as above. But, one is the most recent N₁ samples taken over asliding window, and the other is a long term average, using N₂ samples.So both a long term average and a short term average are maintained.Referring to FIG. 52, the confidence interval around the long termaverage is very small. The error in the estimate is almost completelyremoved. Therefore, the potential uncertain outcomes in the decision arereduced.

In FIG. 53, when the user is moving away from the AP, the upper edge ofthe right confidence interval will fall below the long term average(which has essentially a confidence interval of close to ±0 db.) For agiven application, one needs to ascertain how many samples (N₂) must betaken such that the long term average estimate has essentially 0 error.Also, it is desirable to ascertain how few samples (N₁) are needed inthe short term average to be able to make a decision with 99% accuracy.

Assume a user starts at a position 1 foot away from the AP and movestowards the edge of the 10 ft cell. The goal is to find out how fewsamples are required to ascertain that the user is moving with 99%accuracy, in order to produce the most robust implementation from anoverall performance perspective. If it were possible to “perfectly”measure power, a −6 db drop would be observed each time the user doubleshis distance from the AP. Referring to FIG. 54, if the power level is−38 dbm when the user is at 1 foot, it is −44 dbm at 2 feet and −50 dbmat 4 feet which is almost at the edge of the cell. As can be seen in theFigure, when the short term average is −50 dbm and the upper edge of the99% confidence interval is just below −38 dbm, then the confidenceinterval has a width of ±12 db. To achieve such a confidence interval,14 samples (N₁) are required in the short term, given the previouslyassumed standard deviation of the data, σ=15 db. With these 14 samples,the 99% confidence interval is −60.7 dbm<−50<−39.2 dbm.

In this wireless network example, it has been assumed that a user canwalk from the center of the cell to the edge of the cell in 1.5 seconds.So, samples need be taken every 1.5÷14≈100 milliseconds. As a furtherimprovement, it would be desirable to use 16 samples so that divisioncan be done by a processor via a shift operation. This increasescomputational efficiency on the user's machine. This increases thesample rate a negligible amount.

Regarding the long term average, it may be reasonable to tolerate a±1 dbconfidence interval around the long term estimate. The tighter thisinterval needs to be, the longer the user has to stay near the AP, orstay relatively stationary within a certain area, to cause the averageto converge. It is desirable to calculate how little time the user needsto stay in place to achieve an accuracy of ±1 db with 99% confidence.Assume, reasonably, that signal strength samples are taken based onmessages received from the AP every 50 milliseconds. Referring to thetable shown in FIG. 54, it is seen that if the user stays near the AP (1ft) for about 1.5 minutes, and samples occur every 50 milliseconds, theaccuracy of the power estimate becomes less than ±1 db.

The preferred implementation for the current wireless network examplethus utilizes: (a) a short term average over N₁=16 samples, (b) a longterm average over 2048 samples, and (c) “N₂” which is the number ofsamples taken so far in computing the long term average. The process isas follows:

-   (1) continually calculate the long term average. The long term    average is not “stable” until at least 2000 samples have been taken.    This takes 1.5 minutes at 50 milliseconds per sample. An    implementation preferably accumulates 2048 samples to make the    division a shift operation.-   (2) calculate a short term average with the most recent N₁=16    samples. (16 is used instead of 14 so that the division is    accomplished via a shift.)-   (3) When the difference between the short term and long term    averages is greater than 12 db then it is known with 99% accuracy    that the user is moving.-   (4) When the user roams to a new AP, the counter used to calculate    the long term average samples is reset to 0. Then the long term    average is not stable again for another 2048 samples.

In an environment where users tend to remain in a cell for less than 1second, the long term estimate could be used based on fewer samples.However, this will result in an increased risk of false positives.Several alternatives can be considered to mitigate the occurrence offalse positives:

-   (1) if the user has just arrived in a new cell (i.e. N₂≦32) then    require at least 32 samples before allowing a power-based roaming    decision. This puts some hysteresis into the system. There will be    some false positives though. If the user roams to a new AP and then    back to the old one, false positives may be occurring. It may then    help to require that N₂≦64 for example. This helps the confidence    interval making it −42.8 dbm<−38<−33.1 dbm.-   (2) Take into account the signaling rate. For example, the long term    average accumulates while the number of samples (N₂) grows. But, if    the user's data rate has dropped, then the user has moved outside    the 54 Mbps inner circle by definition. Roaming should be initiated    at this point.-   (3) Once a user has roamed to a new cell, the user should become    “sticky” and try to stay there until the user is near the edge of    the cell. Here it may be useful to require that N₂≧128, for example,    plus see the data rate drop.

To generalize, in a system wherein particular dynamic attributes are tobe ascertained (e.g. “is the wireless network user in motion”), shortterm and long term averages of a system variable (e.g. signal strength)are calculated. An acceptable difference between the short and long termaverages is calculated which positively identifies the systemcharacteristic (e.g. the user has moved.)

Referring to FIG. 55, the steps are generally as follows:

-   1. Define a system dynamic attribute to be ascertained (step 600).    For example, in the wireless network example, the dynamic attribute    to be ascertained is whether a user is moving. In the network usage    example, the dynamic attribute to be ascertained is whether    bandwidth for a user should be increased.-   2. Define a system variable to be monitored to ascertain the dynamic    attribute (step 602). For example, in the wireless network example,    the variable is received signal strength. In the network usage    example, the variable could be number of packets injected onto the    network by the user.-   3. Ascertain the statistical characteristics of the system variable    measurements (step 604). This will include specification and    analysis of individual system and environmental factors that    contribute to statistical variations in the system variable(s). In    the wireless network example, the standard deviation of the signal    strength measurement is affected by environmental noise,    implementation imprecision, spatial events and motion. In the    network usage example the standard deviation is affected by the    degree of burstiness in the traffic generated by the user, the speed    of the user's computer, contention and interleaving effects with    other network traffic, and higher layer network protocol parameters.-   4. Choose the range of the true mean for the system variable that    would indicate that the dynamic system attribute has been identified    (step 606). For example, in the wireless network example, when the    true mean of the signal strength has changed by 12 db, the system    attribute—the user has moved—has been positively identified. In the    network usage example, one may decide that when the true mean for    number of packets injected into the network by a user has exceeded a    threshold, the user's bandwidth should be increased.-   5. Pick a confidence interval based on the accuracy of decisions to    be made regarding the dynamic system attribute (step 608). The rate    of “false positive” decisions and “false negative” decisions is    controlled by how accurately the dynamic system attribute is    estimated. Calculating that attribute with a higher confidence    interval improves that accuracy. In the wireless network example,    the confidence interval was 99%.-   6. Calculate the number of samples of the variable that must be    taken such that the confidence interval around a given metric (such    as the average) results in a spread that is minimized to a    pre-determined amount based on the decision accuracy desired (step    610). In the wireless network example, this was +/−1 db.-   7. Set a long term average based on at least the number of samples    obtained in step 6 (step 612). (This average is cumulative as    opposed to a moving window.)-   8. Given the range chosen in step 4, calculate the number of samples    of the variable that must be taken such that the confidence interval    around a given metric (such as the average) results in a spread that    is less than the range (step 613). This calculation depends upon the    standard deviation in a known manner. This calculation is well known    in the field of statistics as “sample size estimation”. Statistical    studies which use a subset (N) of members of a population need to be    designed so that inferences taken from the sample set are    statistically significant and representative of the entire    population. Specific knowledge, or implicit assumptions, regarding    the statistical characteristics of the dynamic system variables    obtained in Step 3 are used to compute the sample set size. For more    information on known statistical methods for sample size    computation, reference is made to “Statistical Analysis”, Sam Kash    Kachigan, Radius Press, NY 1986 (ISBN: 0-942154-99-1), and in    particular to Section 8-11, pg 157, “Parameter Estimation, Sample    Size Selection for Limiting Error”, and Section 9-10, pg 189,    “Sample Size Selection for Desired Power”-   9. Set a short term average moving window based on the number of    samples obtained in step 8 (step 614).-   10. Calculate the absolute difference between the long term average    and the short term average (step 516). If the difference is greater    than the range chosen in step 4, then the dynamic system attribute    has been positively identified (step 618). In the wireless network    example, when the difference exceeded the range, it was known with    99% confidence that the user was moving or had moved. In the network    usage example, if the difference between short term average packet    count and long term average packet count exceeds the chosen range,    this indicates that the user should be granted higher bandwidth. If    the difference between the long term average and the short term    average is greater than the range chosen in step 4, then the dynamic    system attribute has not been positively identified (step 620), and    N1 moving window samples continue to be collected.

In FIG. 56 there is shown a block diagram showing a wireless networkingsystem that implements the invention. A user (STA 16) communicates withan AP 12 over the wireless network. The user sends messages to the APthat indicate the received signal strength from the AP as perceived bythe user. These messages are collected by the AP (640). A processor 642in the AP uses the messages to compute the short and long term averagesaccording to the process as described in FIG. 55. When it is ascertainedthat the user has moved, an indication 644 is set.

In FIG. 57 there is shown a block diagram of a preferred embodiment of awireless networking system that implements the invention. A user device(STA 16) communicates with an AP over the wireless network. The usermessage collection mechanism 646 receives messages from the AP andmonitors the received signal strength of the messages. A processor orhardware state machine 648 in the user device uses the signal strengthof the messages to compute the short and long term averages according tothe process as described in FIG. 55. When the user device ascertainsthat it is moving, the user sends an indication or message 650 to the APrequesting to roam.

In FIG. 58 there is shown one mechanism that can be used by theprocessor in the implementations of either FIG. 56 or FIG. 57 tomaintain the short and long term averages needed to perform the processof FIG. 55 to ascertain movement. Two ring buffers 652 and 654 aremaintained—one for the short term average and one for the long termaverage. Ring buffers are used so that power sample averaging can beaccomplished over a sliding window in time. In a ring buffer, as a newsampled is added to the buffer, the oldest sample is removed. In thewireless networking example previously described, the short term averagering buffer stores the most recent 16 samples, and the long term averagering buffer stores on the order of 1024 or 2048 samples. Of course thesesample sizes will vary depending on the application. It may also bereasonable to use an accumulator-based average for the long termaverage, but such an approach could be subject to buffer overflow.

A short term average 656 and long term average 658 are calculated basedon the contents of the respective ring buffers 652 and 654. A comparator660 uses a stored allowed range 662 and the short term average 556 andlong term average 658 to produce the movement indication 650 inaccordance with the process of FIG. 55.

In FIG. 59 there is shown an alternate mechanism that can be used by theprocessor in either FIG. 57 or FIG. 56 to maintain the short and longterm averages needed to perform the process of FIG. 55 to ascertainmovement. According to this mechanism, a ring buffer accumulates a smallnumber of samples, for example 16, for computation of the short termaverage. Each short term average computation is saved (656 a-656 n).After a certain number of short term averages have been computed andsaved, the long term average is computed as the average of all theaccumulated short term averages. This approach is known as “batchedmeans”. This approach is advantageous for use in systems containinglimited memory resources.

Though the above described aspects of the invention have beenexemplified as they apply to wireless networks and, in someparticularity, 802.11 networks, it will be clear to the skilledpractitioner that the invention can be employed in any wirelesscommunications environment, including wireless data networks, wirelessphone networks, and wireless I/O channels. All aspects of the inventionmay be implemented in either hardware or software. The preferredembodiment has been described as a software architecture because of itsadvantageous ease of portability between various hardware platforms.

It will be understood that each block of the flowchart illustrations,and combinations of blocks in the flowchart illustrations, can beimplemented by computer program instructions. These computer programinstructions may be loaded onto a computer, embedded devicemicroprocessor (such as that found in an AP or STA), or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions which execute on the computer or other programmabledata processing apparatus create means for implementing the functionsspecified in the flowchart block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function specified in theflowchart block or blocks. The computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed on the computeror other programmable apparatus to produce a computer implementedprocess such that the instructions which execute on the computer orother programmable apparatus provide steps for implementing thefunctions specified in the flowchart block or blocks.

Those skilled in the art should readily appreciate that programsdefining the functions of the present invention can be delivered to acomputer in many forms; including, but not limited to: (a) informationpermanently stored on non-writable storage media (e.g. read only memorydevices within a computer such as ROM or CD-ROM disks readable by acomputer I/O attachment); (b) information alterably stored on writablestorage media (e.g. floppy disks and hard drives); or (c) informationconveyed to a computer through communication media for example usingbaseband signaling or broadband signaling techniques, including carrierwave signaling techniques, such as over computer or telephone networksvia a modem.

While the invention is described through the above exemplaryembodiments, it will be understood by those of ordinary skill in the artthat modification to and variation of the illustrated embodiments may bemade without departing from the inventive concepts herein disclosed.Moreover, while the preferred embodiments are described in connectionwith various illustrative program command structures, one skilled in theart will recognize that the system may be embodied using a variety ofspecific command structures. Accordingly, the invention should not beviewed as limited except by the scope and spirit of the appended claims.

1. A method for use by a first wireless device in a wirelesscommunications environment to evaluate the distance between the firstwireless device and a second wireless device, and the first wirelessdevice and a third wireless device, the method comprising the steps of:calculating a corrected distance from the first wireless device to thethird wireless device based on a first distance to the second wirelessdevice averaged over a first sample size, a second distance to the thirdwireless device averaged over a second sample size, and a first errorvalue related to the first sample size and a second error value relatedto the second sample size; wherein the corrected distance is the firstdistance if the first distance minus the second distance is less than orequal to the total of the first error value plus the second error value;wherein the corrected distance is the second distance if the firstdistance minus the second distance is greater than the total of thefirst error value plus the second error value; using the correcteddistance to ascertain a data rate; using the data rate to ascertain aload factor; calculating a biased distance to the third device equal to(corrected distance * (load factor + (a known load factor related to thesecond device) )/load factor; calculating a biased distance to thesecond device equal to the (first distance * (the known load factorrelated to the second device)/(the known load factor related to thesecond device) + load factor); calculating a biased distance delta equalto the biased distance delta to the second device minus the biaseddistance delta to the third device; requesting association with thethird device if the biased distance delta is positive.
 2. The method ofclaim 1 wherein the step of using the corrected distance to ascertain adata rate does so based on the corrected distance and the wirelesstechnology used in the wireless communications environment.
 3. Themethod of claim 2 wherein the load factor is ascertained based on thedata rate and the wireless technology used in the wirelesscommunications environment.